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	$38.28	5.177%	$40.2618	$40.26	$40.25	$40.30
Purchase #2	$124.48	10.303%	$137.3052	$137.31	$137.30	$137.30
Purchase #3	$106.31	12.456%	$119.552	$119.55	$119.55	$119.60
Purchase #4	$139.30	11.109%	$154.7748	$154.77	$154.75	$154.80
Purchase #5	$233.69	9.257%	$255.3227	$255.32	$255.30	$255.30
Purchase #6	$77.54	4.347%	$80.9107	$80.91	$80.90	$80.90
Purchase #7	$143.91	10.527%	$159.0594	$159.06	$159.05	$159.10
7 purchase totals =	$863.51		$947.1866	$947.18	$947.10	$947.30