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	$74.33	7.754%	$80.0935	$80.09	$80.10	$80.10
Purchase #2	$104.48	6.654%	$111.4321	$111.43	$111.45	$111.40
Purchase #3	$36.30	3.117%	$37.4315	$37.43	$37.45	$37.40
Purchase #4	$37.66	10.210%	$41.5051	$41.51	$41.50	$41.50
Purchase #5	$28.97	11.517%	$32.3065	$32.31	$32.30	$32.30
Purchase #6	$23.57	8.444%	$25.5603	$25.56	$25.55	$25.60
Purchase #7	$115.37	7.795%	$124.3631	$124.36	$124.35	$124.40
7 purchase totals =	$420.68		$452.6921	$452.69	$452.70	$452.70