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	$69.82	11.502%	$77.8507	$77.85	$77.85	$77.90
Purchase #2	$100.54	12.847%	$113.4564	$113.46	$113.45	$113.50
Purchase #3	$119.26	10.663%	$131.9767	$131.98	$132.00	$132.00
Purchase #4	$29.80	3.758%	$30.9199	$30.92	$30.90	$30.90
Purchase #5	$14.83	8.513%	$16.0925	$16.09	$16.10	$16.10
Purchase #6	$82.69	8.244%	$89.507	$89.51	$89.50	$89.50
Purchase #7	$80.28	12.192%	$90.0677	$90.07	$90.05	$90.10
7 purchase totals =	$497.22		$549.8709	$549.88	$549.85	$550.00