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	$126.80	3.595%	$131.3585	$131.36	$131.35	$131.40
Purchase #2	$211.75	8.191%	$229.0944	$229.09	$229.10	$229.10
Purchase #3	$67.31	6.261%	$71.5243	$71.52	$71.50	$71.50
Purchase #4	$26.52	11.324%	$29.5231	$29.52	$29.50	$29.50
Purchase #5	$11.53	4.443%	$12.0423	$12.04	$12.05	$12.00
Purchase #6	$6.55	8.758%	$7.1236	$7.12	$7.10	$7.10
Purchase #7	$38.29	8.838%	$41.6741	$41.67	$41.65	$41.70
7 purchase totals =	$488.75		$522.3403	$522.32	$522.25	$522.30