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	$122.59	7.451%	$131.7242	$131.72	$131.70	$131.70
Purchase #2	$80.40	7.385%	$86.3375	$86.34	$86.35	$86.30
Purchase #3	$245.49	12.404%	$275.9406	$275.94	$275.95	$275.90
Purchase #4	$99.97	11.240%	$111.2066	$111.21	$111.20	$111.20
Purchase #5	$229.98	11.619%	$256.7014	$256.70	$256.70	$256.70
Purchase #6	$108.48	9.820%	$119.1327	$119.13	$119.15	$119.10
Purchase #7	$142.54	5.329%	$150.136	$150.14	$150.15	$150.10
7 purchase totals =	$1,029.45		$1,131.1790	$1,131.18	$1,131.20	$1,131.00