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	$101.59	7.341%	$109.0477	$109.05	$109.05	$109.00
Purchase #2	$42.75	13.557%	$48.5456	$48.55	$48.55	$48.50
Purchase #3	$37.99	11.821%	$42.4808	$42.48	$42.50	$42.50
Purchase #4	$122.58	12.480%	$137.878	$137.88	$137.90	$137.90
Purchase #5	$160.80	12.318%	$180.6073	$180.61	$180.60	$180.60
Purchase #6	$216.87	11.141%	$241.0315	$241.03	$241.05	$241.00
Purchase #7	$217.60	11.430%	$242.4717	$242.47	$242.45	$242.50
7 purchase totals =	$900.18		$1,002.0626	$1,002.07	$1,002.10	$1,002.00