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	$45.25	8.404%	$49.0528	$49.05	$49.05	$49.10
Purchase #2	$174.54	10.489%	$192.8475	$192.85	$192.85	$192.80
Purchase #3	$243.46	13.196%	$275.587	$275.59	$275.60	$275.60
Purchase #4	$137.96	11.244%	$153.4722	$153.47	$153.45	$153.50
Purchase #5	$95.60	4.394%	$99.8007	$99.80	$99.80	$99.80
Purchase #6	$218.48	9.424%	$239.0696	$239.07	$239.05	$239.10
Purchase #7	$65.64	7.682%	$70.6825	$70.68	$70.70	$70.70
7 purchase totals =	$980.93		$1,080.5123	$1,080.51	$1,080.50	$1,080.60