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	$50.57	11.618%	$56.4452	$56.45	$56.45	$56.40
Purchase #2	$64.46	12.327%	$72.406	$72.41	$72.40	$72.40
Purchase #3	$77.38	13.516%	$87.8387	$87.84	$87.85	$87.80
Purchase #4	$127.32	13.148%	$144.06	$144.06	$144.05	$144.10
Purchase #5	$142.38	13.571%	$161.7024	$161.70	$161.70	$161.70
Purchase #6	$76.96	12.201%	$86.3499	$86.35	$86.35	$86.30
Purchase #7	$210.50	5.662%	$222.4185	$222.42	$222.40	$222.40
7 purchase totals =	$749.57		$831.2207	$831.23	$831.20	$831.10