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	$75.37	10.375%	$83.1896	$83.19	$83.20	$83.20
Purchase #2	$67.28	6.856%	$71.8927	$71.89	$71.90	$71.90
Purchase #3	$137.46	7.536%	$147.819	$147.82	$147.80	$147.80
Purchase #4	$44.51	11.431%	$49.5979	$49.60	$49.60	$49.60
Purchase #5	$152.60	3.604%	$158.0997	$158.10	$158.10	$158.10
Purchase #6	$31.53	6.401%	$33.5482	$33.55	$33.55	$33.50
Purchase #7	$160.28	3.577%	$166.0132	$166.01	$166.00	$166.00
7 purchase totals =	$669.03		$710.1603	$710.16	$710.15	$710.10