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	$86.51	9.690%	$94.8928	$94.89	$94.90	$94.90
Purchase #2	$229.53	10.620%	$253.9061	$253.91	$253.90	$253.90
Purchase #3	$130.30	8.164%	$140.9377	$140.94	$140.95	$140.90
Purchase #4	$155.47	10.349%	$171.5596	$171.56	$171.55	$171.60
Purchase #5	$181.95	10.549%	$201.1439	$201.14	$201.15	$201.10
Purchase #6	$40.32	4.840%	$42.2715	$42.27	$42.25	$42.30
Purchase #7	$244.99	9.214%	$267.5634	$267.56	$267.55	$267.60
7 purchase totals =	$1,069.07		$1,172.2750	$1,172.27	$1,172.25	$1,172.30