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	$131.44	8.688%	$142.8595	$142.86	$142.85	$142.90
Purchase #2	$234.67	8.131%	$253.751	$253.75	$253.75	$253.80
Purchase #3	$243.52	3.300%	$251.5562	$251.56	$251.55	$251.60
Purchase #4	$66.25	7.327%	$71.1041	$71.10	$71.10	$71.10
Purchase #5	$12.34	5.453%	$13.0129	$13.01	$13.00	$13.00
Purchase #6	$145.79	8.785%	$158.5977	$158.60	$158.60	$158.60
Purchase #7	$113.74	12.232%	$127.6527	$127.65	$127.65	$127.70
7 purchase totals =	$947.75		$1,018.5341	$1,018.53	$1,018.50	$1,018.70