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	$172.61	7.640%	$185.7974	$185.80	$185.80	$185.80
Purchase #2	$138.45	5.426%	$145.9623	$145.96	$145.95	$146.00
Purchase #3	$48.90	5.192%	$51.4389	$51.44	$51.45	$51.40
Purchase #4	$129.46	7.780%	$139.532	$139.53	$139.55	$139.50
Purchase #5	$208.63	3.710%	$216.3702	$216.37	$216.35	$216.40
Purchase #6	$84.39	9.390%	$92.3142	$92.31	$92.30	$92.30
Purchase #7	$39.49	3.561%	$40.8962	$40.90	$40.90	$40.90
7 purchase totals =	$821.93		$872.3112	$872.31	$872.30	$872.30