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	$203.63	9.305%	$222.5778	$222.58	$222.60	$222.60
Purchase #2	$96.57	11.325%	$107.5066	$107.51	$107.50	$107.50
Purchase #3	$102.37	13.155%	$115.8368	$115.84	$115.85	$115.80
Purchase #4	$223.95	11.735%	$250.2305	$250.23	$250.25	$250.20
Purchase #5	$206.46	8.243%	$223.4785	$223.48	$223.50	$223.50
Purchase #6	$48.58	9.162%	$53.0309	$53.03	$53.05	$53.00
Purchase #7	$163.28	11.759%	$182.4801	$182.48	$182.50	$182.50
7 purchase totals =	$1,044.84		$1,155.1412	$1,155.15	$1,155.25	$1,155.10