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	$121.29	6.254%	$128.8755	$128.88	$128.90	$128.90
Purchase #2	$231.99	10.501%	$256.3513	$256.35	$256.35	$256.40
Purchase #3	$74.57	13.331%	$84.5109	$84.51	$84.50	$84.50
Purchase #4	$144.71	9.800%	$158.8916	$158.89	$158.90	$158.90
Purchase #5	$231.55	8.725%	$251.7527	$251.75	$251.75	$251.80
Purchase #6	$40.34	4.428%	$42.1263	$42.13	$42.15	$42.10
Purchase #7	$127.69	8.640%	$138.7224	$138.72	$138.70	$138.70
7 purchase totals =	$972.14		$1,061.2307	$1,061.23	$1,061.25	$1,061.30