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	$46.88	7.747%	$50.5118	$50.51	$50.50	$50.50
Purchase #2	$106.90	3.789%	$110.9504	$110.95	$110.95	$111.00
Purchase #3	$151.92	6.161%	$161.2798	$161.28	$161.30	$161.30
Purchase #4	$25.62	12.753%	$28.8873	$28.89	$28.90	$28.90
Purchase #5	$57.65	3.586%	$59.7173	$59.72	$59.70	$59.70
Purchase #6	$41.84	8.664%	$45.465	$45.47	$45.45	$45.50
Purchase #7	$31.39	7.353%	$33.6981	$33.70	$33.70	$33.70
7 purchase totals =	$462.20		$490.5097	$490.52	$490.50	$490.60