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	$99.78	10.847%	$110.6031	$110.60	$110.60	$110.60
Purchase #2	$48.46	13.352%	$54.9304	$54.93	$54.95	$54.90
Purchase #3	$37.47	8.499%	$40.6546	$40.65	$40.65	$40.70
Purchase #4	$223.84	7.472%	$240.5653	$240.57	$240.55	$240.60
Purchase #5	$208.52	6.809%	$222.7181	$222.72	$222.70	$222.70
Purchase #6	$74.50	12.598%	$83.8855	$83.89	$83.90	$83.90
Purchase #7	$69.26	4.328%	$72.2576	$72.26	$72.25	$72.30
7 purchase totals =	$761.83		$825.6146	$825.62	$825.60	$825.70