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	$231.84	10.653%	$256.5379	$256.54	$256.55	$256.50
Purchase #2	$38.64	5.641%	$40.8197	$40.82	$40.80	$40.80
Purchase #3	$25.64	7.816%	$27.644	$27.64	$27.65	$27.60
Purchase #4	$94.65	9.800%	$103.9257	$103.93	$103.95	$103.90
Purchase #5	$78.70	13.635%	$89.4307	$89.43	$89.45	$89.40
Purchase #6	$220.90	13.746%	$251.2649	$251.26	$251.25	$251.30
Purchase #7	$64.86	10.756%	$71.8363	$71.84	$71.85	$71.80
7 purchase totals =	$755.23		$841.4592	$841.46	$841.50	$841.30