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	$142.73	13.652%	$162.2155	$162.22	$162.20	$162.20
Purchase #2	$123.78	13.810%	$140.874	$140.87	$140.85	$140.90
Purchase #3	$49.60	11.413%	$55.2608	$55.26	$55.25	$55.30
Purchase #4	$40.72	12.670%	$45.8792	$45.88	$45.90	$45.90
Purchase #5	$139.81	13.227%	$158.3027	$158.30	$158.30	$158.30
Purchase #6	$107.61	13.530%	$122.1696	$122.17	$122.15	$122.20
Purchase #7	$122.53	10.589%	$135.5047	$135.50	$135.50	$135.50
7 purchase totals =	$726.78		$820.2065	$820.20	$820.15	$820.30