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	$33.53	12.780%	$37.8151	$37.82	$37.80	$37.80
Purchase #2	$114.83	11.444%	$127.9711	$127.97	$127.95	$128.00
Purchase #3	$134.33	13.267%	$152.1516	$152.15	$152.15	$152.20
Purchase #4	$57.57	7.501%	$61.8883	$61.89	$61.90	$61.90
Purchase #5	$211.59	4.566%	$221.2512	$221.25	$221.25	$221.30
Purchase #6	$108.43	3.594%	$112.327	$112.33	$112.35	$112.30
Purchase #7	$204.77	9.246%	$223.703	$223.70	$223.70	$223.70
7 purchase totals =	$865.05		$937.1073	$937.11	$937.10	$937.20