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	$82.25	10.392%	$90.7974	$90.80	$90.80	$90.80
Purchase #2	$148.89	12.762%	$167.8913	$167.89	$167.90	$167.90
Purchase #3	$247.43	13.136%	$279.9324	$279.93	$279.95	$279.90
Purchase #4	$84.53	13.311%	$95.7818	$95.78	$95.80	$95.80
Purchase #5	$166.63	7.707%	$179.4722	$179.47	$179.45	$179.50
Purchase #6	$192.82	4.427%	$201.3561	$201.36	$201.35	$201.40
Purchase #7	$137.62	13.789%	$156.5964	$156.60	$156.60	$156.60
7 purchase totals =	$1,060.17		$1,171.8276	$1,171.83	$1,171.85	$1,171.90