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	$80.98	3.261%	$83.6208	$83.62	$83.60	$83.60
Purchase #2	$33.44	13.488%	$37.9504	$37.95	$37.95	$38.00
Purchase #3	$139.55	7.184%	$149.5753	$149.58	$149.60	$149.60
Purchase #4	$208.62	4.229%	$217.4425	$217.44	$217.45	$217.40
Purchase #5	$160.70	4.826%	$168.4554	$168.46	$168.45	$168.50
Purchase #6	$128.79	13.693%	$146.4252	$146.43	$146.45	$146.40
Purchase #7	$216.64	11.872%	$242.3595	$242.36	$242.35	$242.40
7 purchase totals =	$968.72		$1,045.8291	$1,045.84	$1,045.85	$1,045.90