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	$142.74	11.230%	$158.7697	$158.77	$158.75	$158.80
Purchase #2	$143.76	9.148%	$156.9112	$156.91	$156.90	$156.90
Purchase #3	$106.77	9.653%	$117.0765	$117.08	$117.10	$117.10
Purchase #4	$35.35	6.162%	$37.5283	$37.53	$37.55	$37.50
Purchase #5	$93.64	8.346%	$101.4552	$101.46	$101.45	$101.50
Purchase #6	$65.90	11.700%	$73.6103	$73.61	$73.60	$73.60
Purchase #7	$30.85	10.773%	$34.1735	$34.17	$34.15	$34.20
7 purchase totals =	$619.01		$679.5247	$679.53	$679.50	$679.60