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	$114.74	11.762%	$128.2357	$128.24	$128.25	$128.20
Purchase #2	$164.81	8.844%	$179.3858	$179.39	$179.40	$179.40
Purchase #3	$83.47	5.182%	$87.7954	$87.80	$87.80	$87.80
Purchase #4	$37.56	8.164%	$40.6264	$40.63	$40.65	$40.60
Purchase #5	$85.25	5.361%	$89.8203	$89.82	$89.80	$89.80
Purchase #6	$188.94	11.797%	$211.2293	$211.23	$211.25	$211.20
Purchase #7	$54.50	9.699%	$59.786	$59.79	$59.80	$59.80
7 purchase totals =	$729.27		$796.8789	$796.90	$796.95	$796.80