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	$8.26	11.150%	$9.181	$9.18	$9.20	$9.20
Purchase #2	$144.41	5.105%	$151.7821	$151.78	$151.80	$151.80
Purchase #3	$131.30	7.546%	$141.2079	$141.21	$141.20	$141.20
Purchase #4	$99.61	5.574%	$105.1623	$105.16	$105.15	$105.20
Purchase #5	$39.98	6.121%	$42.4272	$42.43	$42.45	$42.40
Purchase #6	$240.52	12.428%	$270.4118	$270.41	$270.40	$270.40
Purchase #7	$159.41	11.870%	$178.332	$178.33	$178.35	$178.30
7 purchase totals =	$823.49		$898.5043	$898.50	$898.55	$898.50