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	$36.83	9.181%	$40.2114	$40.21	$40.20	$40.20
Purchase #2	$230.95	10.534%	$255.2783	$255.28	$255.30	$255.30
Purchase #3	$152.45	9.162%	$166.4175	$166.42	$166.40	$166.40
Purchase #4	$64.71	7.325%	$69.45	$69.45	$69.45	$69.50
Purchase #5	$112.28	11.775%	$125.501	$125.50	$125.50	$125.50
Purchase #6	$103.61	12.427%	$116.4856	$116.49	$116.50	$116.50
Purchase #7	$165.79	3.576%	$171.7187	$171.72	$171.70	$171.70
7 purchase totals =	$866.62		$945.0625	$945.07	$945.05	$945.10