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	$37.91	11.616%	$42.3136	$42.31	$42.30	$42.30
Purchase #2	$223.38	7.373%	$239.8498	$239.85	$239.85	$239.80
Purchase #3	$227.63	12.277%	$255.5761	$255.58	$255.60	$255.60
Purchase #4	$229.40	9.365%	$250.8833	$250.88	$250.90	$250.90
Purchase #5	$100.29	7.198%	$107.5089	$107.51	$107.50	$107.50
Purchase #6	$83.81	5.542%	$88.4548	$88.45	$88.45	$88.50
Purchase #7	$82.72	5.820%	$87.5343	$87.53	$87.55	$87.50
7 purchase totals =	$985.14		$1,072.1208	$1,072.11	$1,072.15	$1,072.10