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	$175.85	8.556%	$190.8957	$190.90	$190.90	$190.90
Purchase #2	$84.33	7.814%	$90.9195	$90.92	$90.90	$90.90
Purchase #3	$197.69	12.526%	$222.4526	$222.45	$222.45	$222.50
Purchase #4	$151.45	13.458%	$171.8321	$171.83	$171.85	$171.80
Purchase #5	$223.29	11.694%	$249.4015	$249.40	$249.40	$249.40
Purchase #6	$83.48	8.197%	$90.3229	$90.32	$90.30	$90.30
Purchase #7	$204.45	3.486%	$211.5771	$211.58	$211.60	$211.60
7 purchase totals =	$1,120.54		$1,227.4014	$1,227.40	$1,227.40	$1,227.40