Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$71.69	10.167%	$78.9787	$78.98	$79.00	$79.00
Purchase #2	$211.48	4.578%	$221.1616	$221.16	$221.15	$221.20
Purchase #3	$39.33	8.820%	$42.7989	$42.80	$42.80	$42.80
Purchase #4	$11.90	7.442%	$12.7856	$12.79	$12.80	$12.80
Purchase #5	$247.57	13.298%	$280.4919	$280.49	$280.50	$280.50
Purchase #6	$137.57	12.581%	$154.8777	$154.88	$154.90	$154.90
Purchase #7	$114.83	10.849%	$127.2879	$127.29	$127.30	$127.30
7 purchase totals =	$834.37		$918.3823	$918.39	$918.45	$918.50