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	$29.82	10.388%	$32.9177	$32.92	$32.90	$32.90
Purchase #2	$79.92	13.260%	$90.5174	$90.52	$90.50	$90.50
Purchase #3	$153.30	9.780%	$168.2927	$168.29	$168.30	$168.30
Purchase #4	$172.63	9.691%	$189.3596	$189.36	$189.35	$189.40
Purchase #5	$37.56	8.721%	$40.8356	$40.84	$40.85	$40.80
Purchase #6	$81.25	8.354%	$88.0376	$88.04	$88.05	$88.00
Purchase #7	$53.78	8.434%	$58.3158	$58.32	$58.30	$58.30
7 purchase totals =	$608.26		$668.2764	$668.29	$668.25	$668.20