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	$243.48	5.429%	$256.6985	$256.70	$256.70	$256.70
Purchase #2	$154.83	3.829%	$160.7584	$160.76	$160.75	$160.80
Purchase #3	$157.45	7.629%	$169.4619	$169.46	$169.45	$169.50
Purchase #4	$242.57	4.570%	$253.6554	$253.66	$253.65	$253.70
Purchase #5	$203.36	6.600%	$216.7818	$216.78	$216.80	$216.80
Purchase #6	$227.32	10.165%	$250.4271	$250.43	$250.45	$250.40
Purchase #7	$177.45	8.561%	$192.6415	$192.64	$192.65	$192.60
7 purchase totals =	$1,406.46		$1,500.4246	$1,500.43	$1,500.45	$1,500.50