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	$122.35	13.850%	$139.2955	$139.30	$139.30	$139.30
Purchase #2	$173.88	12.128%	$194.9682	$194.97	$194.95	$195.00
Purchase #3	$229.33	13.780%	$260.9317	$260.93	$260.95	$260.90
Purchase #4	$222.58	11.767%	$248.771	$248.77	$248.75	$248.80
Purchase #5	$141.83	8.534%	$153.9338	$153.93	$153.95	$153.90
Purchase #6	$174.53	12.384%	$196.1438	$196.14	$196.15	$196.10
Purchase #7	$151.45	9.299%	$165.5333	$165.53	$165.55	$165.50
7 purchase totals =	$1,215.95		$1,359.5773	$1,359.57	$1,359.60	$1,359.50