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	$11.98	4.389%	$12.5058	$12.51	$12.50	$12.50
Purchase #2	$67.70	5.683%	$71.5474	$71.55	$71.55	$71.50
Purchase #3	$119.83	9.567%	$131.2941	$131.29	$131.30	$131.30
Purchase #4	$106.49	8.291%	$115.3191	$115.32	$115.30	$115.30
Purchase #5	$185.92	12.766%	$209.6545	$209.65	$209.65	$209.70
Purchase #6	$41.55	11.483%	$46.3212	$46.32	$46.30	$46.30
Purchase #7	$33.40	7.504%	$35.9063	$35.91	$35.90	$35.90
7 purchase totals =	$566.87		$622.5484	$622.55	$622.50	$622.50