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	$22.81	13.496%	$25.8884	$25.89	$25.90	$25.90
Purchase #2	$32.30	4.394%	$33.7193	$33.72	$33.70	$33.70
Purchase #3	$80.96	11.849%	$90.553	$90.55	$90.55	$90.60
Purchase #4	$41.32	6.740%	$44.105	$44.11	$44.10	$44.10
Purchase #5	$99.38	5.809%	$105.153	$105.15	$105.15	$105.20
Purchase #6	$87.37	3.647%	$90.5564	$90.56	$90.55	$90.60
Purchase #7	$152.89	11.503%	$170.4769	$170.48	$170.50	$170.50
7 purchase totals =	$517.03		$560.4520	$560.46	$560.45	$560.60