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	$81.84	10.273%	$90.2474	$90.25	$90.25	$90.20
Purchase #2	$94.49	4.459%	$98.7033	$98.70	$98.70	$98.70
Purchase #3	$187.49	8.746%	$203.8879	$203.89	$203.90	$203.90
Purchase #4	$165.34	6.390%	$175.9052	$175.91	$175.90	$175.90
Purchase #5	$161.40	11.685%	$180.2596	$180.26	$180.25	$180.30
Purchase #6	$141.82	11.409%	$158.0002	$158.00	$158.00	$158.00
Purchase #7	$183.25	3.362%	$189.4109	$189.41	$189.40	$189.40
7 purchase totals =	$1,015.63		$1,096.4145	$1,096.42	$1,096.40	$1,096.40