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	$38.75	3.704%	$40.1853	$40.19	$40.20	$40.20
Purchase #2	$139.60	9.225%	$152.4781	$152.48	$152.50	$152.50
Purchase #3	$132.42	13.303%	$150.0358	$150.04	$150.05	$150.00
Purchase #4	$195.38	10.804%	$216.4889	$216.49	$216.50	$216.50
Purchase #5	$50.59	9.484%	$55.388	$55.39	$55.40	$55.40
Purchase #6	$160.71	7.363%	$172.5431	$172.54	$172.55	$172.50
Purchase #7	$81.83	8.313%	$88.6325	$88.63	$88.65	$88.60
7 purchase totals =	$799.28		$875.7517	$875.76	$875.85	$875.70