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	$54.36	9.255%	$59.391	$59.39	$59.40	$59.40
Purchase #2	$36.67	10.120%	$40.381	$40.38	$40.40	$40.40
Purchase #3	$220.45	3.345%	$227.8241	$227.82	$227.80	$227.80
Purchase #4	$141.27	6.592%	$150.5825	$150.58	$150.60	$150.60
Purchase #5	$219.44	12.618%	$247.1289	$247.13	$247.15	$247.10
Purchase #6	$228.82	6.486%	$243.6613	$243.66	$243.65	$243.70
Purchase #7	$66.45	7.785%	$71.6231	$71.62	$71.60	$71.60
7 purchase totals =	$967.46		$1,040.5919	$1,040.58	$1,040.60	$1,040.60