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	$136.43	12.469%	$153.4415	$153.44	$153.45	$153.40
Purchase #2	$125.90	10.459%	$139.0679	$139.07	$139.05	$139.10
Purchase #3	$242.72	7.751%	$261.5332	$261.53	$261.55	$261.50
Purchase #4	$101.43	13.856%	$115.4841	$115.48	$115.50	$115.50
Purchase #5	$22.99	12.381%	$25.8364	$25.84	$25.85	$25.80
Purchase #6	$161.94	6.301%	$172.1438	$172.14	$172.15	$172.10
Purchase #7	$71.47	9.771%	$78.4533	$78.45	$78.45	$78.50
7 purchase totals =	$862.88		$945.9602	$945.95	$946.00	$945.90