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	$163.90	4.255%	$170.8739	$170.87	$170.85	$170.90
Purchase #2	$243.61	12.577%	$274.2488	$274.25	$274.25	$274.20
Purchase #3	$23.50	13.673%	$26.7132	$26.71	$26.70	$26.70
Purchase #4	$57.30	4.455%	$59.8527	$59.85	$59.85	$59.90
Purchase #5	$104.83	9.847%	$115.1526	$115.15	$115.15	$115.20
Purchase #6	$93.52	7.237%	$100.288	$100.29	$100.30	$100.30
Purchase #7	$182.95	7.565%	$196.7902	$196.79	$196.80	$196.80
7 purchase totals =	$869.61		$943.9194	$943.91	$943.90	$944.00