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	$36.66	7.251%	$39.3182	$39.32	$39.30	$39.30
Purchase #2	$88.44	12.776%	$99.7391	$99.74	$99.75	$99.70
Purchase #3	$186.86	9.871%	$205.305	$205.31	$205.30	$205.30
Purchase #4	$75.91	8.401%	$82.2872	$82.29	$82.30	$82.30
Purchase #5	$31.43	12.426%	$35.3355	$35.34	$35.35	$35.30
Purchase #6	$55.58	10.874%	$61.6238	$61.62	$61.60	$61.60
Purchase #7	$94.44	6.873%	$100.9309	$100.93	$100.95	$100.90
7 purchase totals =	$569.32		$624.5397	$624.55	$624.55	$624.40