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	$146.44	13.477%	$166.1757	$166.18	$166.20	$166.20
Purchase #2	$40.48	6.488%	$43.1063	$43.11	$43.10	$43.10
Purchase #3	$181.46	12.633%	$204.3838	$204.38	$204.40	$204.40
Purchase #4	$143.26	13.541%	$162.6588	$162.66	$162.65	$162.70
Purchase #5	$140.94	10.262%	$155.4033	$155.40	$155.40	$155.40
Purchase #6	$144.74	9.486%	$158.47	$158.47	$158.45	$158.50
Purchase #7	$58.70	4.222%	$61.1783	$61.18	$61.20	$61.20
7 purchase totals =	$856.02		$951.3762	$951.38	$951.40	$951.50