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	$167.70	4.217%	$174.7719	$174.77	$174.75	$174.80
Purchase #2	$142.39	9.705%	$156.2089	$156.21	$156.20	$156.20
Purchase #3	$110.34	10.673%	$122.1166	$122.12	$122.10	$122.10
Purchase #4	$125.35	11.573%	$139.8568	$139.86	$139.85	$139.90
Purchase #5	$185.47	12.625%	$208.8856	$208.89	$208.90	$208.90
Purchase #6	$115.37	10.521%	$127.5081	$127.51	$127.50	$127.50
Purchase #7	$66.90	3.624%	$69.3245	$69.32	$69.30	$69.30
7 purchase totals =	$913.52		$998.6724	$998.68	$998.60	$998.70