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	$39.59	6.302%	$42.085	$42.09	$42.10	$42.10
Purchase #2	$34.25	7.130%	$36.692	$36.69	$36.70	$36.70
Purchase #3	$246.76	13.288%	$279.5495	$279.55	$279.55	$279.50
Purchase #4	$162.74	10.164%	$179.2809	$179.28	$179.30	$179.30
Purchase #5	$202.94	9.363%	$221.9413	$221.94	$221.95	$221.90
Purchase #6	$234.45	4.698%	$245.4645	$245.46	$245.45	$245.50
Purchase #7	$17.52	3.760%	$18.1788	$18.18	$18.20	$18.20
7 purchase totals =	$938.25		$1,023.1920	$1,023.19	$1,023.25	$1,023.20