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	$72.35	12.252%	$81.2143	$81.21	$81.20	$81.20
Purchase #2	$152.66	7.763%	$164.511	$164.51	$164.50	$164.50
Purchase #3	$154.84	7.169%	$165.9405	$165.94	$165.95	$165.90
Purchase #4	$250.61	13.260%	$283.8409	$283.84	$283.85	$283.80
Purchase #5	$19.81	10.525%	$21.895	$21.90	$21.90	$21.90
Purchase #6	$127.72	10.119%	$140.644	$140.64	$140.65	$140.60
Purchase #7	$141.93	6.480%	$151.1271	$151.13	$151.15	$151.10
7 purchase totals =	$919.92		$1,009.1728	$1,009.17	$1,009.20	$1,009.00