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	$73.56	3.561%	$76.1795	$76.18	$76.20	$76.20
Purchase #2	$53.65	11.480%	$59.809	$59.81	$59.80	$59.80
Purchase #3	$73.53	11.502%	$81.9874	$81.99	$82.00	$82.00
Purchase #4	$139.54	8.289%	$151.1065	$151.11	$151.10	$151.10
Purchase #5	$89.55	9.859%	$98.3787	$98.38	$98.40	$98.40
Purchase #6	$99.89	8.727%	$108.6074	$108.61	$108.60	$108.60
Purchase #7	$53.79	11.148%	$59.7865	$59.79	$59.80	$59.80
7 purchase totals =	$583.51		$635.8550	$635.87	$635.90	$635.90