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	$55.86	6.518%	$59.501	$59.50	$59.50	$59.50
Purchase #2	$11.83	7.555%	$12.7238	$12.72	$12.70	$12.70
Purchase #3	$155.53	11.202%	$172.9525	$172.95	$172.95	$173.00
Purchase #4	$155.52	7.104%	$166.5681	$166.57	$166.55	$166.60
Purchase #5	$89.83	5.812%	$95.0509	$95.05	$95.05	$95.10
Purchase #6	$173.85	8.767%	$189.0914	$189.09	$189.10	$189.10
Purchase #7	$169.76	5.223%	$178.6266	$178.63	$178.65	$178.60
7 purchase totals =	$812.18		$874.5143	$874.51	$874.50	$874.60