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	$138.74	12.165%	$155.6177	$155.62	$155.60	$155.60
Purchase #2	$68.89	13.624%	$78.2756	$78.28	$78.30	$78.30
Purchase #3	$19.50	6.522%	$20.7718	$20.77	$20.75	$20.80
Purchase #4	$247.76	6.507%	$263.8817	$263.88	$263.90	$263.90
Purchase #5	$210.28	10.114%	$231.5477	$231.55	$231.55	$231.50
Purchase #6	$55.83	10.179%	$61.5129	$61.51	$61.50	$61.50
Purchase #7	$143.65	7.576%	$154.5329	$154.53	$154.55	$154.50
7 purchase totals =	$884.65		$966.1403	$966.14	$966.15	$966.10