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	$42.66	7.180%	$45.723	$45.72	$45.70	$45.70
Purchase #2	$68.28	9.594%	$74.8308	$74.83	$74.85	$74.80
Purchase #3	$233.82	6.203%	$248.3239	$248.32	$248.30	$248.30
Purchase #4	$192.89	5.411%	$203.3273	$203.33	$203.35	$203.30
Purchase #5	$45.69	3.565%	$47.3188	$47.32	$47.30	$47.30
Purchase #6	$67.96	5.808%	$71.9071	$71.91	$71.90	$71.90
Purchase #7	$155.36	6.775%	$165.8856	$165.89	$165.90	$165.90
7 purchase totals =	$806.66		$857.3165	$857.32	$857.30	$857.20