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	$128.91	13.403%	$146.1878	$146.19	$146.20	$146.20
Purchase #2	$80.61	5.643%	$85.1588	$85.16	$85.15	$85.20
Purchase #3	$204.42	11.645%	$228.2247	$228.22	$228.20	$228.20
Purchase #4	$143.73	10.634%	$159.0142	$159.01	$159.00	$159.00
Purchase #5	$71.33	9.667%	$78.2255	$78.23	$78.25	$78.20
Purchase #6	$248.85	13.566%	$282.609	$282.61	$282.60	$282.60
Purchase #7	$87.83	12.222%	$98.5646	$98.56	$98.55	$98.60
7 purchase totals =	$965.68		$1,077.9846	$1,077.98	$1,077.95	$1,078.00