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	$20.60	4.124%	$21.4495	$21.45	$21.45	$21.40
Purchase #2	$102.98	11.260%	$114.5755	$114.58	$114.60	$114.60
Purchase #3	$202.97	8.844%	$220.9207	$220.92	$220.90	$220.90
Purchase #4	$85.55	3.558%	$88.5939	$88.59	$88.60	$88.60
Purchase #5	$73.72	5.680%	$77.9073	$77.91	$77.90	$77.90
Purchase #6	$37.56	13.784%	$42.7373	$42.74	$42.75	$42.70
Purchase #7	$55.44	5.682%	$58.5901	$58.59	$58.60	$58.60
7 purchase totals =	$578.82		$624.7743	$624.78	$624.80	$624.70