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	$89.61	3.202%	$92.4793	$92.48	$92.50	$92.50
Purchase #2	$106.54	4.272%	$111.0914	$111.09	$111.10	$111.10
Purchase #3	$130.94	7.221%	$140.3952	$140.40	$140.40	$140.40
Purchase #4	$60.25	6.809%	$64.3524	$64.35	$64.35	$64.40
Purchase #5	$32.54	6.650%	$34.7039	$34.70	$34.70	$34.70
Purchase #6	$56.37	11.300%	$62.7398	$62.74	$62.75	$62.70
Purchase #7	$170.52	12.285%	$191.4684	$191.47	$191.45	$191.50
7 purchase totals =	$646.77		$697.2304	$697.23	$697.25	$697.30