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	$56.52	7.857%	$60.9608	$60.96	$60.95	$61.00
Purchase #2	$78.90	13.803%	$89.7906	$89.79	$89.80	$89.80
Purchase #3	$8.36	13.221%	$9.4653	$9.47	$9.45	$9.50
Purchase #4	$20.26	10.808%	$22.4497	$22.45	$22.45	$22.40
Purchase #5	$101.46	3.381%	$104.8904	$104.89	$104.90	$104.90
Purchase #6	$127.58	7.503%	$137.1523	$137.15	$137.15	$137.20
Purchase #7	$76.51	12.436%	$86.0248	$86.02	$86.00	$86.00
7 purchase totals =	$469.59		$510.7339	$510.73	$510.70	$510.80