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	$240.77	5.292%	$253.5115	$253.51	$253.50	$253.50
Purchase #2	$150.99	12.173%	$169.37	$169.37	$169.35	$169.40
Purchase #3	$145.47	3.662%	$150.7971	$150.80	$150.80	$150.80
Purchase #4	$70.38	3.539%	$72.8707	$72.87	$72.85	$72.90
Purchase #5	$160.85	5.225%	$169.2544	$169.25	$169.25	$169.30
Purchase #6	$39.91	13.747%	$45.3964	$45.40	$45.40	$45.40
Purchase #7	$71.29	10.610%	$78.8539	$78.85	$78.85	$78.90
7 purchase totals =	$879.66		$940.0540	$940.05	$940.00	$940.20