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	$55.69	7.133%	$59.6624	$59.66	$59.65	$59.70
Purchase #2	$67.59	10.375%	$74.6025	$74.60	$74.60	$74.60
Purchase #3	$40.95	12.688%	$46.1457	$46.15	$46.15	$46.10
Purchase #4	$170.83	8.178%	$184.8005	$184.80	$184.80	$184.80
Purchase #5	$190.45	11.569%	$212.4832	$212.48	$212.50	$212.50
Purchase #6	$32.73	4.123%	$34.0795	$34.08	$34.10	$34.10
Purchase #7	$52.45	6.586%	$55.9044	$55.90	$55.90	$55.90
7 purchase totals =	$610.69		$667.6782	$667.67	$667.70	$667.70