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	$45.36	12.197%	$50.8926	$50.89	$50.90	$50.90
Purchase #2	$170.59	5.857%	$180.5815	$180.58	$180.60	$180.60
Purchase #3	$91.59	13.244%	$103.7202	$103.72	$103.70	$103.70
Purchase #4	$53.78	6.302%	$57.1692	$57.17	$57.15	$57.20
Purchase #5	$192.27	3.747%	$199.4744	$199.47	$199.45	$199.50
Purchase #6	$6.74	9.270%	$7.3648	$7.36	$7.35	$7.40
Purchase #7	$43.39	5.537%	$45.7925	$45.79	$45.80	$45.80
7 purchase totals =	$603.72		$644.9952	$644.98	$644.95	$645.10