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	$149.36	11.792%	$166.9725	$166.97	$166.95	$167.00
Purchase #2	$147.30	6.766%	$157.2663	$157.27	$157.25	$157.30
Purchase #3	$116.91	8.800%	$127.1981	$127.20	$127.20	$127.20
Purchase #4	$75.76	7.537%	$81.47	$81.47	$81.45	$81.50
Purchase #5	$195.51	11.760%	$218.502	$218.50	$218.50	$218.50
Purchase #6	$27.59	3.654%	$28.5981	$28.60	$28.60	$28.60
Purchase #7	$83.59	8.456%	$90.6584	$90.66	$90.65	$90.70
7 purchase totals =	$796.02		$870.6654	$870.67	$870.60	$870.80