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	$9.90	10.303%	$10.92	$10.92	$10.90	$10.90
Purchase #2	$20.25	3.145%	$20.8869	$20.89	$20.90	$20.90
Purchase #3	$176.29	11.192%	$196.0204	$196.02	$196.00	$196.00
Purchase #4	$207.29	8.409%	$224.721	$224.72	$224.70	$224.70
Purchase #5	$74.90	13.241%	$84.8175	$84.82	$84.80	$84.80
Purchase #6	$125.63	9.427%	$137.4731	$137.47	$137.45	$137.50
Purchase #7	$183.62	4.360%	$191.6258	$191.63	$191.65	$191.60
7 purchase totals =	$797.88		$866.4647	$866.47	$866.40	$866.40