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	$172.79	10.586%	$191.0815	$191.08	$191.10	$191.10
Purchase #2	$126.50	8.581%	$137.355	$137.36	$137.35	$137.40
Purchase #3	$129.64	10.433%	$143.1653	$143.17	$143.15	$143.20
Purchase #4	$159.83	4.366%	$166.8082	$166.81	$166.80	$166.80
Purchase #5	$40.43	8.111%	$43.7093	$43.71	$43.70	$43.70
Purchase #6	$43.76	8.360%	$47.4183	$47.42	$47.40	$47.40
Purchase #7	$136.43	11.323%	$151.878	$151.88	$151.90	$151.90
7 purchase totals =	$809.38		$881.4156	$881.43	$881.40	$881.50