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	$239.44	12.775%	$270.0285	$270.03	$270.05	$270.00
Purchase #2	$16.74	10.576%	$18.5104	$18.51	$18.50	$18.50
Purchase #3	$243.58	5.442%	$256.8356	$256.84	$256.85	$256.80
Purchase #4	$152.79	4.702%	$159.9742	$159.97	$159.95	$160.00
Purchase #5	$19.35	9.805%	$21.2473	$21.25	$21.25	$21.20
Purchase #6	$85.38	5.845%	$90.3705	$90.37	$90.35	$90.40
Purchase #7	$59.59	13.130%	$67.4142	$67.41	$67.40	$67.40
7 purchase totals =	$816.87		$884.3807	$884.38	$884.35	$884.30