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	$31.56	6.501%	$33.6117	$33.61	$33.60	$33.60
Purchase #2	$27.96	12.672%	$31.5031	$31.50	$31.50	$31.50
Purchase #3	$227.98	10.416%	$251.7264	$251.73	$251.75	$251.70
Purchase #4	$138.90	4.178%	$144.7032	$144.70	$144.70	$144.70
Purchase #5	$229.91	13.343%	$260.5869	$260.59	$260.60	$260.60
Purchase #6	$171.89	5.502%	$181.3474	$181.35	$181.35	$181.30
Purchase #7	$29.81	7.340%	$31.9981	$32.00	$32.00	$32.00
7 purchase totals =	$858.01		$935.4768	$935.48	$935.50	$935.40