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	$78.92	13.595%	$89.6492	$89.65	$89.65	$89.60
Purchase #2	$173.42	13.197%	$196.3062	$196.31	$196.30	$196.30
Purchase #3	$246.95	8.333%	$267.5283	$267.53	$267.55	$267.50
Purchase #4	$106.81	10.521%	$118.0475	$118.05	$118.05	$118.00
Purchase #5	$165.53	13.304%	$187.5521	$187.55	$187.55	$187.60
Purchase #6	$109.84	7.521%	$118.1011	$118.10	$118.10	$118.10
Purchase #7	$239.89	6.672%	$255.8955	$255.90	$255.90	$255.90
7 purchase totals =	$1,121.36		$1,233.0799	$1,233.09	$1,233.10	$1,233.00