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	$129.80	10.570%	$143.5199	$143.52	$143.50	$143.50
Purchase #2	$161.67	13.138%	$182.9102	$182.91	$182.90	$182.90
Purchase #3	$159.70	10.794%	$176.938	$176.94	$176.95	$176.90
Purchase #4	$244.73	3.565%	$253.4546	$253.45	$253.45	$253.50
Purchase #5	$136.78	9.773%	$150.1475	$150.15	$150.15	$150.10
Purchase #6	$192.33	12.590%	$216.5443	$216.54	$216.55	$216.50
Purchase #7	$143.42	8.774%	$156.0037	$156.00	$156.00	$156.00
7 purchase totals =	$1,168.43		$1,279.5182	$1,279.51	$1,279.50	$1,279.40