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	$75.77	10.222%	$83.5152	$83.52	$83.50	$83.50
Purchase #2	$114.71	4.337%	$119.685	$119.69	$119.70	$119.70
Purchase #3	$80.26	12.288%	$90.1223	$90.12	$90.10	$90.10
Purchase #4	$50.65	8.368%	$54.8884	$54.89	$54.90	$54.90
Purchase #5	$232.41	9.717%	$254.9933	$254.99	$255.00	$255.00
Purchase #6	$131.58	13.128%	$148.8538	$148.85	$148.85	$148.90
Purchase #7	$20.38	10.746%	$22.57	$22.57	$22.55	$22.60
7 purchase totals =	$705.76		$774.6280	$774.63	$774.60	$774.70