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	$33.95	6.632%	$36.2016	$36.20	$36.20	$36.20
Purchase #2	$133.65	8.275%	$144.7095	$144.71	$144.70	$144.70
Purchase #3	$40.33	11.685%	$45.0426	$45.04	$45.05	$45.00
Purchase #4	$65.50	10.476%	$72.3618	$72.36	$72.35	$72.40
Purchase #5	$108.72	10.137%	$119.7409	$119.74	$119.75	$119.70
Purchase #6	$39.65	3.125%	$40.8891	$40.89	$40.90	$40.90
Purchase #7	$164.79	9.696%	$180.768	$180.77	$180.75	$180.80
7 purchase totals =	$586.59		$639.7135	$639.71	$639.70	$639.70