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	$109.89	6.397%	$116.9197	$116.92	$116.90	$116.90
Purchase #2	$223.40	4.257%	$232.9101	$232.91	$232.90	$232.90
Purchase #3	$227.93	8.153%	$246.5131	$246.51	$246.50	$246.50
Purchase #4	$128.38	12.495%	$144.4211	$144.42	$144.40	$144.40
Purchase #5	$225.37	11.109%	$250.4064	$250.41	$250.40	$250.40
Purchase #6	$58.68	3.456%	$60.708	$60.71	$60.70	$60.70
Purchase #7	$66.66	7.555%	$71.6962	$71.70	$71.70	$71.70
7 purchase totals =	$1,040.31		$1,123.5746	$1,123.58	$1,123.50	$1,123.50