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	$229.89	11.161%	$255.548	$255.55	$255.55	$255.50
Purchase #2	$55.78	13.689%	$63.4157	$63.42	$63.40	$63.40
Purchase #3	$124.25	9.560%	$136.1283	$136.13	$136.15	$136.10
Purchase #4	$97.47	5.210%	$102.5482	$102.55	$102.55	$102.50
Purchase #5	$106.87	4.766%	$111.9634	$111.96	$111.95	$112.00
Purchase #6	$170.46	5.401%	$179.6665	$179.67	$179.65	$179.70
Purchase #7	$242.32	13.342%	$274.6503	$274.65	$274.65	$274.70
7 purchase totals =	$1,027.04		$1,123.9204	$1,123.93	$1,123.90	$1,123.90