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	$121.46	11.694%	$135.6635	$135.66	$135.65	$135.70
Purchase #2	$214.70	13.307%	$243.2701	$243.27	$243.25	$243.30
Purchase #3	$40.51	4.369%	$42.2799	$42.28	$42.30	$42.30
Purchase #4	$189.61	3.624%	$196.4815	$196.48	$196.50	$196.50
Purchase #5	$58.82	11.409%	$65.5308	$65.53	$65.55	$65.50
Purchase #6	$250.89	11.412%	$279.5216	$279.52	$279.50	$279.50
Purchase #7	$33.97	8.218%	$36.7617	$36.76	$36.75	$36.80
7 purchase totals =	$909.96		$999.5091	$999.50	$999.50	$999.60