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	$133.37	13.360%	$151.1882	$151.19	$151.20	$151.20
Purchase #2	$244.67	9.705%	$268.4152	$268.42	$268.40	$268.40
Purchase #3	$234.83	11.105%	$260.9079	$260.91	$260.90	$260.90
Purchase #4	$10.96	8.479%	$11.8893	$11.89	$11.90	$11.90
Purchase #5	$117.74	11.727%	$131.5474	$131.55	$131.55	$131.50
Purchase #6	$138.92	7.160%	$148.8667	$148.87	$148.85	$148.90
Purchase #7	$80.32	12.860%	$90.6492	$90.65	$90.65	$90.60
7 purchase totals =	$960.81		$1,063.4639	$1,063.48	$1,063.45	$1,063.40