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	$90.61	10.647%	$100.2572	$100.26	$100.25	$100.30
Purchase #2	$119.28	3.847%	$123.8687	$123.87	$123.85	$123.90
Purchase #3	$178.30	6.741%	$190.3192	$190.32	$190.30	$190.30
Purchase #4	$125.94	11.587%	$140.5327	$140.53	$140.55	$140.50
Purchase #5	$197.81	11.642%	$220.839	$220.84	$220.85	$220.80
Purchase #6	$69.58	9.145%	$75.9431	$75.94	$75.95	$75.90
Purchase #7	$137.89	10.197%	$151.9506	$151.95	$151.95	$152.00
7 purchase totals =	$919.41		$1,003.7105	$1,003.71	$1,003.70	$1,003.70