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	$200.38	10.197%	$220.8127	$220.81	$220.80	$220.80
Purchase #2	$111.79	8.643%	$121.452	$121.45	$121.45	$121.50
Purchase #3	$233.88	3.788%	$242.7394	$242.74	$242.75	$242.70
Purchase #4	$243.29	11.339%	$270.8767	$270.88	$270.90	$270.90
Purchase #5	$63.61	12.165%	$71.3482	$71.35	$71.35	$71.30
Purchase #6	$132.65	5.492%	$139.9351	$139.94	$139.95	$139.90
Purchase #7	$65.25	11.767%	$72.928	$72.93	$72.95	$72.90
7 purchase totals =	$1,050.85		$1,140.0921	$1,140.10	$1,140.15	$1,140.00