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	$34.49	9.286%	$37.6927	$37.69	$37.70	$37.70
Purchase #2	$75.38	11.283%	$83.8851	$83.89	$83.90	$83.90
Purchase #3	$93.45	12.678%	$105.2976	$105.30	$105.30	$105.30
Purchase #4	$18.42	8.465%	$19.9793	$19.98	$20.00	$20.00
Purchase #5	$127.70	7.550%	$137.3414	$137.34	$137.35	$137.30
Purchase #6	$202.28	13.501%	$229.5898	$229.59	$229.60	$229.60
Purchase #7	$85.29	6.134%	$90.5217	$90.52	$90.50	$90.50
7 purchase totals =	$637.01		$704.3076	$704.31	$704.35	$704.30