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	$180.59	8.729%	$196.3537	$196.35	$196.35	$196.40
Purchase #2	$11.58	13.462%	$13.1389	$13.14	$13.15	$13.10
Purchase #3	$243.69	13.167%	$275.7767	$275.78	$275.80	$275.80
Purchase #4	$225.89	12.849%	$254.9146	$254.91	$254.90	$254.90
Purchase #5	$134.43	4.265%	$140.1634	$140.16	$140.15	$140.20
Purchase #6	$75.39	9.711%	$82.7111	$82.71	$82.70	$82.70
Purchase #7	$14.52	12.188%	$16.2897	$16.29	$16.30	$16.30
7 purchase totals =	$886.09		$979.3481	$979.34	$979.35	$979.40