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	$51.65	10.369%	$57.0056	$57.01	$57.00	$57.00
Purchase #2	$105.69	7.736%	$113.8662	$113.87	$113.85	$113.90
Purchase #3	$85.60	5.798%	$90.5631	$90.56	$90.55	$90.60
Purchase #4	$142.41	3.192%	$146.9557	$146.96	$146.95	$147.00
Purchase #5	$91.95	9.201%	$100.4103	$100.41	$100.40	$100.40
Purchase #6	$219.42	9.756%	$240.8266	$240.83	$240.85	$240.80
Purchase #7	$129.71	12.776%	$146.2817	$146.28	$146.30	$146.30
7 purchase totals =	$826.43		$895.9092	$895.92	$895.90	$896.00