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	$166.88	10.151%	$183.82	$183.82	$183.80	$183.80
Purchase #2	$170.48	11.873%	$190.7211	$190.72	$190.70	$190.70
Purchase #3	$137.96	12.609%	$155.3554	$155.36	$155.35	$155.40
Purchase #4	$220.83	12.812%	$249.1227	$249.12	$249.10	$249.10
Purchase #5	$141.26	7.206%	$151.4392	$151.44	$151.45	$151.40
Purchase #6	$78.57	4.484%	$82.0931	$82.09	$82.10	$82.10
Purchase #7	$87.86	5.754%	$92.9155	$92.92	$92.90	$92.90
7 purchase totals =	$1,003.84		$1,105.4670	$1,105.47	$1,105.40	$1,105.40