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	$30.77	5.756%	$32.5411	$32.54	$32.55	$32.50
Purchase #2	$90.31	10.497%	$99.7898	$99.79	$99.80	$99.80
Purchase #3	$9.44	11.454%	$10.5213	$10.52	$10.50	$10.50
Purchase #4	$95.33	5.188%	$100.2757	$100.28	$100.30	$100.30
Purchase #5	$241.49	13.743%	$274.678	$274.68	$274.70	$274.70
Purchase #6	$222.36	8.761%	$241.841	$241.84	$241.85	$241.80
Purchase #7	$33.77	6.817%	$36.0721	$36.07	$36.05	$36.10
7 purchase totals =	$723.47		$795.7190	$795.72	$795.75	$795.70