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	$90.29	11.797%	$100.9415	$100.94	$100.95	$100.90
Purchase #2	$164.49	6.606%	$175.3562	$175.36	$175.35	$175.40
Purchase #3	$79.82	12.367%	$89.6913	$89.69	$89.70	$89.70
Purchase #4	$174.51	8.422%	$189.2072	$189.21	$189.20	$189.20
Purchase #5	$68.64	10.847%	$76.0854	$76.09	$76.10	$76.10
Purchase #6	$229.27	13.686%	$260.6479	$260.65	$260.65	$260.60
Purchase #7	$159.85	7.501%	$171.8403	$171.84	$171.85	$171.80
7 purchase totals =	$966.87		$1,063.7698	$1,063.78	$1,063.80	$1,063.70