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	$88.48	6.357%	$94.1047	$94.10	$94.10	$94.10
Purchase #2	$42.62	7.599%	$45.8587	$45.86	$45.85	$45.90
Purchase #3	$13.52	3.858%	$14.0416	$14.04	$14.05	$14.00
Purchase #4	$141.79	3.156%	$146.2649	$146.26	$146.25	$146.30
Purchase #5	$18.81	6.153%	$19.9674	$19.97	$19.95	$20.00
Purchase #6	$117.60	5.646%	$124.2397	$124.24	$124.25	$124.20
Purchase #7	$55.85	5.804%	$59.0915	$59.09	$59.10	$59.10
7 purchase totals =	$478.67		$503.5685	$503.56	$503.55	$503.60