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	$180.59	6.123%	$191.6475	$191.65	$191.65	$191.60
Purchase #2	$208.39	7.200%	$223.3941	$223.39	$223.40	$223.40
Purchase #3	$33.37	8.230%	$36.1164	$36.12	$36.10	$36.10
Purchase #4	$215.74	11.279%	$240.0733	$240.07	$240.05	$240.10
Purchase #5	$140.74	3.125%	$145.1381	$145.14	$145.15	$145.10
Purchase #6	$238.86	13.518%	$271.1491	$271.15	$271.15	$271.10
Purchase #7	$29.34	12.485%	$33.0031	$33.00	$33.00	$33.00
7 purchase totals =	$1,047.03		$1,140.5216	$1,140.52	$1,140.50	$1,140.40