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	$220.30	8.402%	$238.8096	$238.81	$238.80	$238.80
Purchase #2	$31.74	13.419%	$35.9992	$36.00	$36.00	$36.00
Purchase #3	$40.77	7.468%	$43.8147	$43.81	$43.80	$43.80
Purchase #4	$88.58	7.527%	$95.2474	$95.25	$95.25	$95.20
Purchase #5	$63.59	3.563%	$65.8557	$65.86	$65.85	$65.90
Purchase #6	$17.48	6.162%	$18.5571	$18.56	$18.55	$18.60
Purchase #7	$38.67	4.155%	$40.2767	$40.28	$40.30	$40.30
7 purchase totals =	$501.13		$538.5604	$538.57	$538.55	$538.60