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	$110.66	9.223%	$120.8662	$120.87	$120.85	$120.90
Purchase #2	$47.81	13.762%	$54.3896	$54.39	$54.40	$54.40
Purchase #3	$199.33	3.405%	$206.1172	$206.12	$206.10	$206.10
Purchase #4	$236.67	3.312%	$244.5085	$244.51	$244.50	$244.50
Purchase #5	$53.90	10.330%	$59.4679	$59.47	$59.45	$59.50
Purchase #6	$242.48	10.770%	$268.5951	$268.60	$268.60	$268.60
Purchase #7	$39.67	3.273%	$40.9684	$40.97	$40.95	$41.00
7 purchase totals =	$930.52		$994.9129	$994.93	$994.85	$995.00