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	$96.89	10.291%	$106.8609	$106.86	$106.85	$106.90
Purchase #2	$152.98	5.547%	$161.4658	$161.47	$161.45	$161.50
Purchase #3	$125.46	4.282%	$130.8322	$130.83	$130.85	$130.80
Purchase #4	$236.81	11.365%	$263.7235	$263.72	$263.70	$263.70
Purchase #5	$42.40	7.287%	$45.4897	$45.49	$45.50	$45.50
Purchase #6	$249.66	12.116%	$279.9088	$279.91	$279.90	$279.90
Purchase #7	$10.57	3.122%	$10.9	$10.90	$10.90	$10.90
7 purchase totals =	$914.77		$999.1809	$999.18	$999.15	$999.20