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	$54.57	7.266%	$58.5351	$58.54	$58.55	$58.50
Purchase #2	$140.43	9.562%	$153.8579	$153.86	$153.85	$153.90
Purchase #3	$187.97	8.253%	$203.4832	$203.48	$203.50	$203.50
Purchase #4	$24.32	5.774%	$25.7242	$25.72	$25.70	$25.70
Purchase #5	$35.89	4.195%	$37.3956	$37.40	$37.40	$37.40
Purchase #6	$69.98	3.572%	$72.4797	$72.48	$72.50	$72.50
Purchase #7	$60.62	11.723%	$67.7265	$67.73	$67.75	$67.70
7 purchase totals =	$573.78		$619.2022	$619.21	$619.25	$619.20