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	$138.90	7.610%	$149.4703	$149.47	$149.45	$149.50
Purchase #2	$181.52	8.309%	$196.6025	$196.60	$196.60	$196.60
Purchase #3	$152.48	7.689%	$164.2042	$164.20	$164.20	$164.20
Purchase #4	$32.35	7.729%	$34.8503	$34.85	$34.85	$34.90
Purchase #5	$5.65	12.707%	$6.3679	$6.37	$6.35	$6.40
Purchase #6	$119.72	9.748%	$131.3903	$131.39	$131.40	$131.40
Purchase #7	$29.69	9.662%	$32.5586	$32.56	$32.55	$32.60
7 purchase totals =	$660.31		$715.4441	$715.44	$715.40	$715.60