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	$56.96	6.729%	$60.7928	$60.79	$60.80	$60.80
Purchase #2	$50.87	12.624%	$57.2918	$57.29	$57.30	$57.30
Purchase #3	$241.87	5.490%	$255.1487	$255.15	$255.15	$255.10
Purchase #4	$35.49	13.454%	$40.2648	$40.26	$40.25	$40.30
Purchase #5	$191.64	8.799%	$208.5024	$208.50	$208.50	$208.50
Purchase #6	$221.27	12.548%	$249.035	$249.04	$249.05	$249.00
Purchase #7	$234.46	13.244%	$265.5119	$265.51	$265.50	$265.50
7 purchase totals =	$1,032.56		$1,136.5474	$1,136.54	$1,136.55	$1,136.50