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	$65.32	7.325%	$70.1047	$70.10	$70.10	$70.10
Purchase #2	$59.51	13.261%	$67.4016	$67.40	$67.40	$67.40
Purchase #3	$190.61	13.459%	$216.2642	$216.26	$216.25	$216.30
Purchase #4	$240.55	12.145%	$269.7648	$269.76	$269.75	$269.80
Purchase #5	$133.97	12.665%	$150.9373	$150.94	$150.95	$150.90
Purchase #6	$248.92	10.110%	$274.0858	$274.09	$274.10	$274.10
Purchase #7	$69.51	4.766%	$72.8228	$72.82	$72.80	$72.80
7 purchase totals =	$1,008.39		$1,121.3812	$1,121.37	$1,121.35	$1,121.40