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	$88.54	5.387%	$93.3096	$93.31	$93.30	$93.30
Purchase #2	$120.58	10.209%	$132.89	$132.89	$132.90	$132.90
Purchase #3	$223.86	13.448%	$253.9647	$253.96	$253.95	$254.00
Purchase #4	$81.86	12.575%	$92.1539	$92.15	$92.15	$92.20
Purchase #5	$57.73	6.385%	$61.4161	$61.42	$61.40	$61.40
Purchase #6	$50.35	3.473%	$52.0987	$52.10	$52.10	$52.10
Purchase #7	$33.60	10.628%	$37.171	$37.17	$37.15	$37.20
7 purchase totals =	$656.52		$723.0040	$723.00	$722.95	$723.10