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	$29.72	8.246%	$32.1707	$32.17	$32.15	$32.20
Purchase #2	$65.76	6.367%	$69.9469	$69.95	$69.95	$69.90
Purchase #3	$39.72	8.530%	$43.1081	$43.11	$43.10	$43.10
Purchase #4	$85.66	6.442%	$91.1782	$91.18	$91.20	$91.20
Purchase #5	$149.98	6.503%	$159.7332	$159.73	$159.75	$159.70
Purchase #6	$90.76	10.530%	$100.317	$100.32	$100.30	$100.30
Purchase #7	$23.85	11.259%	$26.5353	$26.54	$26.55	$26.50
7 purchase totals =	$485.45		$522.9894	$523.00	$523.00	$522.90