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	$35.43	5.423%	$37.3514	$37.35	$37.35	$37.40
Purchase #2	$58.50	13.310%	$66.2864	$66.29	$66.30	$66.30
Purchase #3	$175.86	6.240%	$186.8337	$186.83	$186.85	$186.80
Purchase #4	$120.97	12.140%	$135.6558	$135.66	$135.65	$135.70
Purchase #5	$55.58	6.845%	$59.3845	$59.38	$59.40	$59.40
Purchase #6	$185.53	7.653%	$199.7286	$199.73	$199.75	$199.70
Purchase #7	$114.73	13.452%	$130.1635	$130.16	$130.15	$130.20
7 purchase totals =	$746.60		$815.4039	$815.40	$815.45	$815.50