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	$139.51	13.220%	$157.9532	$157.95	$157.95	$158.00
Purchase #2	$151.87	3.134%	$156.6296	$156.63	$156.65	$156.60
Purchase #3	$136.89	9.601%	$150.0328	$150.03	$150.05	$150.00
Purchase #4	$111.43	7.832%	$120.1572	$120.16	$120.15	$120.20
Purchase #5	$179.53	9.245%	$196.1275	$196.13	$196.15	$196.10
Purchase #6	$65.94	8.373%	$71.4612	$71.46	$71.45	$71.50
Purchase #7	$30.78	7.441%	$33.0703	$33.07	$33.05	$33.10
7 purchase totals =	$815.95		$885.4318	$885.43	$885.45	$885.50