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	$125.48	12.522%	$141.1926	$141.19	$141.20	$141.20
Purchase #2	$221.70	7.519%	$238.3696	$238.37	$238.35	$238.40
Purchase #3	$124.80	12.153%	$139.9669	$139.97	$139.95	$140.00
Purchase #4	$38.45	10.253%	$42.3923	$42.39	$42.40	$42.40
Purchase #5	$93.55	7.467%	$100.5354	$100.54	$100.55	$100.50
Purchase #6	$133.75	13.379%	$151.6444	$151.64	$151.65	$151.60
Purchase #7	$20.62	10.819%	$22.8509	$22.85	$22.85	$22.90
7 purchase totals =	$758.35		$836.9521	$836.95	$836.95	$837.00