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	$177.48	12.289%	$199.2905	$199.29	$199.30	$199.30
Purchase #2	$140.80	12.804%	$158.828	$158.83	$158.85	$158.80
Purchase #3	$124.58	13.428%	$141.3086	$141.31	$141.30	$141.30
Purchase #4	$61.56	12.210%	$69.0765	$69.08	$69.10	$69.10
Purchase #5	$127.96	13.648%	$145.424	$145.42	$145.40	$145.40
Purchase #6	$126.96	13.132%	$143.6324	$143.63	$143.65	$143.60
Purchase #7	$137.70	6.229%	$146.2773	$146.28	$146.30	$146.30
7 purchase totals =	$897.04		$1,003.8373	$1,003.84	$1,003.90	$1,003.80