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	$70.60	12.653%	$79.533	$79.53	$79.55	$79.50
Purchase #2	$76.31	13.264%	$86.4318	$86.43	$86.45	$86.40
Purchase #3	$34.47	9.445%	$37.7257	$37.73	$37.75	$37.70
Purchase #4	$157.98	9.297%	$172.6674	$172.67	$172.65	$172.70
Purchase #5	$99.61	13.418%	$112.9757	$112.98	$113.00	$113.00
Purchase #6	$51.48	12.552%	$57.9418	$57.94	$57.95	$57.90
Purchase #7	$78.50	12.269%	$88.1312	$88.13	$88.15	$88.10
7 purchase totals =	$568.95		$635.4066	$635.41	$635.50	$635.30