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	$84.29	7.442%	$90.5629	$90.56	$90.55	$90.60
Purchase #2	$182.90	8.841%	$199.0702	$199.07	$199.05	$199.10
Purchase #3	$133.61	9.221%	$145.9302	$145.93	$145.95	$145.90
Purchase #4	$215.71	7.606%	$232.1169	$232.12	$232.10	$232.10
Purchase #5	$39.35	6.142%	$41.7669	$41.77	$41.75	$41.80
Purchase #6	$84.72	6.248%	$90.0133	$90.01	$90.00	$90.00
Purchase #7	$147.38	4.104%	$153.4285	$153.43	$153.45	$153.40
7 purchase totals =	$887.96		$952.8889	$952.89	$952.85	$952.90