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	$43.83	3.846%	$45.5157	$45.52	$45.50	$45.50
Purchase #2	$18.68	9.214%	$20.4012	$20.40	$20.40	$20.40
Purchase #3	$158.83	9.449%	$173.8378	$173.84	$173.85	$173.80
Purchase #4	$78.86	7.731%	$84.9567	$84.96	$84.95	$85.00
Purchase #5	$124.80	13.501%	$141.6492	$141.65	$141.65	$141.60
Purchase #6	$115.38	13.709%	$131.1974	$131.20	$131.20	$131.20
Purchase #7	$89.90	4.671%	$94.0992	$94.10	$94.10	$94.10
7 purchase totals =	$630.28		$691.6572	$691.67	$691.65	$691.60