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	$242.89	3.278%	$250.8519	$250.85	$250.85	$250.90
Purchase #2	$59.58	9.306%	$65.1245	$65.12	$65.10	$65.10
Purchase #3	$225.56	10.598%	$249.4648	$249.46	$249.45	$249.50
Purchase #4	$67.38	4.351%	$70.3117	$70.31	$70.30	$70.30
Purchase #5	$52.48	6.562%	$55.9237	$55.92	$55.90	$55.90
Purchase #6	$94.77	3.111%	$97.7183	$97.72	$97.70	$97.70
Purchase #7	$48.93	8.610%	$53.1429	$53.14	$53.15	$53.10
7 purchase totals =	$791.59		$842.5378	$842.52	$842.45	$842.50