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	$250.26	12.455%	$281.4299	$281.43	$281.45	$281.40
Purchase #2	$55.68	7.187%	$59.6817	$59.68	$59.70	$59.70
Purchase #3	$199.53	10.327%	$220.1355	$220.14	$220.15	$220.10
Purchase #4	$139.65	13.315%	$158.2444	$158.24	$158.25	$158.20
Purchase #5	$240.76	9.559%	$263.7742	$263.77	$263.75	$263.80
Purchase #6	$37.81	6.142%	$40.1323	$40.13	$40.15	$40.10
Purchase #7	$54.78	5.400%	$57.7381	$57.74	$57.75	$57.70
7 purchase totals =	$978.47		$1,081.1361	$1,081.13	$1,081.20	$1,081.00