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	$91.59	12.828%	$103.3392	$103.34	$103.35	$103.30
Purchase #2	$161.52	9.121%	$176.2522	$176.25	$176.25	$176.30
Purchase #3	$7.93	7.391%	$8.5161	$8.52	$8.50	$8.50
Purchase #4	$131.25	11.119%	$145.8437	$145.84	$145.85	$145.80
Purchase #5	$37.40	12.769%	$42.1756	$42.18	$42.20	$42.20
Purchase #6	$137.82	13.201%	$156.0136	$156.01	$156.00	$156.00
Purchase #7	$145.26	6.792%	$155.1261	$155.13	$155.15	$155.10
7 purchase totals =	$712.77		$787.2665	$787.27	$787.30	$787.20