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	$37.72	11.438%	$42.0344	$42.03	$42.05	$42.00
Purchase #2	$212.41	11.518%	$236.8754	$236.88	$236.90	$236.90
Purchase #3	$84.82	8.781%	$92.268	$92.27	$92.25	$92.30
Purchase #4	$34.87	4.666%	$36.497	$36.50	$36.50	$36.50
Purchase #5	$153.40	13.526%	$174.1489	$174.15	$174.15	$174.10
Purchase #6	$13.37	3.389%	$13.8231	$13.82	$13.80	$13.80
Purchase #7	$159.55	7.286%	$171.1748	$171.17	$171.15	$171.20
7 purchase totals =	$696.14		$766.8216	$766.82	$766.80	$766.80