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	$50.36	4.215%	$52.4827	$52.48	$52.50	$52.50
Purchase #2	$141.75	8.754%	$154.1588	$154.16	$154.15	$154.20
Purchase #3	$60.31	10.574%	$66.6872	$66.69	$66.70	$66.70
Purchase #4	$33.67	5.513%	$35.5262	$35.53	$35.55	$35.50
Purchase #5	$67.46	8.143%	$72.9533	$72.95	$72.95	$73.00
Purchase #6	$42.98	6.146%	$45.6216	$45.62	$45.60	$45.60
Purchase #7	$167.87	10.687%	$185.8103	$185.81	$185.80	$185.80
7 purchase totals =	$564.40		$613.2401	$613.24	$613.25	$613.30