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	$225.84	13.125%	$255.4815	$255.48	$255.50	$255.50
Purchase #2	$84.82	12.456%	$95.3852	$95.39	$95.40	$95.40
Purchase #3	$46.51	12.834%	$52.4791	$52.48	$52.50	$52.50
Purchase #4	$131.35	3.555%	$136.0195	$136.02	$136.00	$136.00
Purchase #5	$165.68	9.544%	$181.4925	$181.49	$181.50	$181.50
Purchase #6	$230.25	6.362%	$244.8985	$244.90	$244.90	$244.90
Purchase #7	$235.74	9.497%	$258.1282	$258.13	$258.15	$258.10
7 purchase totals =	$1,120.19		$1,223.8845	$1,223.89	$1,223.95	$1,223.90