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	$89.36	11.701%	$99.816	$99.82	$99.80	$99.80
Purchase #2	$169.38	6.521%	$180.4253	$180.43	$180.45	$180.40
Purchase #3	$224.70	10.597%	$248.5115	$248.51	$248.50	$248.50
Purchase #4	$64.38	11.380%	$71.7064	$71.71	$71.70	$71.70
Purchase #5	$215.92	8.115%	$233.4419	$233.44	$233.45	$233.40
Purchase #6	$61.83	6.267%	$65.7049	$65.70	$65.70	$65.70
Purchase #7	$9.35	8.105%	$10.1078	$10.11	$10.10	$10.10
7 purchase totals =	$834.92		$909.7138	$909.72	$909.70	$909.60