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	$235.43	12.134%	$263.9971	$264.00	$264.00	$264.00
Purchase #2	$89.79	10.505%	$99.2224	$99.22	$99.20	$99.20
Purchase #3	$185.55	3.418%	$191.8921	$191.89	$191.90	$191.90
Purchase #4	$200.54	13.250%	$227.1116	$227.11	$227.10	$227.10
Purchase #5	$54.89	8.580%	$59.5996	$59.60	$59.60	$59.60
Purchase #6	$236.74	12.317%	$265.8993	$265.90	$265.90	$265.90
Purchase #7	$108.48	12.338%	$121.8643	$121.86	$121.85	$121.90
7 purchase totals =	$1,111.42		$1,229.5864	$1,229.58	$1,229.55	$1,229.60