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	$11.41	10.713%	$12.6324	$12.63	$12.65	$12.60
Purchase #2	$242.97	11.468%	$270.8338	$270.83	$270.85	$270.80
Purchase #3	$223.57	12.251%	$250.9596	$250.96	$250.95	$251.00
Purchase #4	$18.36	4.218%	$19.1344	$19.13	$19.15	$19.10
Purchase #5	$196.59	11.512%	$219.2214	$219.22	$219.20	$219.20
Purchase #6	$105.88	13.807%	$120.4989	$120.50	$120.50	$120.50
Purchase #7	$69.41	13.217%	$78.5839	$78.58	$78.60	$78.60
7 purchase totals =	$868.19		$971.8644	$971.85	$971.90	$971.80