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	$48.36	4.362%	$50.4695	$50.47	$50.45	$50.50
Purchase #2	$20.36	5.412%	$21.4619	$21.46	$21.45	$21.50
Purchase #3	$127.95	13.168%	$144.7985	$144.80	$144.80	$144.80
Purchase #4	$163.29	3.162%	$168.4532	$168.45	$168.45	$168.50
Purchase #5	$19.31	4.633%	$20.2046	$20.20	$20.20	$20.20
Purchase #6	$136.76	11.457%	$152.4286	$152.43	$152.45	$152.40
Purchase #7	$114.28	12.587%	$128.6644	$128.66	$128.65	$128.70
7 purchase totals =	$630.31		$686.4807	$686.47	$686.45	$686.60