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	$39.83	11.589%	$44.4459	$44.45	$44.45	$44.40
Purchase #2	$105.35	10.274%	$116.1737	$116.17	$116.15	$116.20
Purchase #3	$171.31	7.341%	$183.8859	$183.89	$183.90	$183.90
Purchase #4	$212.62	4.196%	$221.5415	$221.54	$221.55	$221.50
Purchase #5	$166.56	12.182%	$186.8503	$186.85	$186.85	$186.90
Purchase #6	$130.57	8.421%	$141.5653	$141.57	$141.55	$141.60
Purchase #7	$58.43	5.867%	$61.8581	$61.86	$61.85	$61.90
7 purchase totals =	$884.67		$956.3207	$956.33	$956.30	$956.40