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	$219.42	4.197%	$228.6291	$228.63	$228.65	$228.60
Purchase #2	$126.46	13.254%	$143.221	$143.22	$143.20	$143.20
Purchase #3	$230.30	9.785%	$252.8349	$252.83	$252.85	$252.80
Purchase #4	$196.44	12.871%	$221.7238	$221.72	$221.70	$221.70
Purchase #5	$113.61	8.735%	$123.5338	$123.53	$123.55	$123.50
Purchase #6	$83.72	6.824%	$89.4331	$89.43	$89.45	$89.40
Purchase #7	$50.25	11.225%	$55.8906	$55.89	$55.90	$55.90
7 purchase totals =	$1,020.20		$1,115.2663	$1,115.25	$1,115.30	$1,115.10