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	$121.66	12.828%	$137.2665	$137.27	$137.25	$137.30
Purchase #2	$155.25	11.400%	$172.9485	$172.95	$172.95	$172.90
Purchase #3	$196.77	9.202%	$214.8768	$214.88	$214.90	$214.90
Purchase #4	$81.67	13.653%	$92.8204	$92.82	$92.80	$92.80
Purchase #5	$132.90	5.327%	$139.9796	$139.98	$140.00	$140.00
Purchase #6	$155.33	7.437%	$166.8819	$166.88	$166.90	$166.90
Purchase #7	$212.83	13.110%	$240.732	$240.73	$240.75	$240.70
7 purchase totals =	$1,056.41		$1,165.5057	$1,165.51	$1,165.55	$1,165.50