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	$224.34	10.257%	$247.3506	$247.35	$247.35	$247.40
Purchase #2	$80.45	11.709%	$89.8699	$89.87	$89.85	$89.90
Purchase #3	$32.50	9.682%	$35.6467	$35.65	$35.65	$35.60
Purchase #4	$47.76	5.117%	$50.2039	$50.20	$50.20	$50.20
Purchase #5	$89.81	7.782%	$96.799	$96.80	$96.80	$96.80
Purchase #6	$186.79	6.808%	$199.5067	$199.51	$199.50	$199.50
Purchase #7	$51.80	9.153%	$56.5413	$56.54	$56.55	$56.50
7 purchase totals =	$713.45		$775.9181	$775.92	$775.90	$775.90