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	$120.37	8.173%	$130.2078	$130.21	$130.20	$130.20
Purchase #2	$14.39	7.834%	$15.5173	$15.52	$15.50	$15.50
Purchase #3	$214.54	13.699%	$243.9298	$243.93	$243.95	$243.90
Purchase #4	$83.35	8.564%	$90.4881	$90.49	$90.50	$90.50
Purchase #5	$125.92	12.684%	$141.8917	$141.89	$141.90	$141.90
Purchase #6	$96.65	7.398%	$103.8002	$103.80	$103.80	$103.80
Purchase #7	$144.91	9.707%	$158.9764	$158.98	$159.00	$159.00
7 purchase totals =	$800.13		$884.8113	$884.82	$884.85	$884.80