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	$82.68	3.332%	$85.4349	$85.43	$85.45	$85.40
Purchase #2	$90.25	10.572%	$99.7912	$99.79	$99.80	$99.80
Purchase #3	$61.42	7.664%	$66.1272	$66.13	$66.15	$66.10
Purchase #4	$84.53	11.604%	$94.3389	$94.34	$94.35	$94.30
Purchase #5	$111.55	5.784%	$118.0021	$118.00	$118.00	$118.00
Purchase #6	$38.59	8.447%	$41.8497	$41.85	$41.85	$41.80
Purchase #7	$247.88	10.672%	$274.3338	$274.33	$274.35	$274.30
7 purchase totals =	$716.90		$779.8778	$779.87	$779.95	$779.70