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	$193.94	11.158%	$215.5798	$215.58	$215.60	$215.60
Purchase #2	$88.66	12.145%	$99.4278	$99.43	$99.45	$99.40
Purchase #3	$210.72	13.486%	$239.1377	$239.14	$239.15	$239.10
Purchase #4	$236.96	9.306%	$259.0115	$259.01	$259.00	$259.00
Purchase #5	$143.91	12.261%	$161.5548	$161.55	$161.55	$161.60
Purchase #6	$51.50	13.556%	$58.4813	$58.48	$58.50	$58.50
Purchase #7	$57.72	3.294%	$59.6213	$59.62	$59.60	$59.60
7 purchase totals =	$983.41		$1,092.8142	$1,092.81	$1,092.85	$1,092.80