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	$69.62	12.296%	$78.1805	$78.18	$78.20	$78.20
Purchase #2	$237.44	10.407%	$262.1504	$262.15	$262.15	$262.20
Purchase #3	$131.44	12.816%	$148.2854	$148.29	$148.30	$148.30
Purchase #4	$98.50	5.752%	$104.1657	$104.17	$104.15	$104.20
Purchase #5	$211.95	12.513%	$238.4713	$238.47	$238.45	$238.50
Purchase #6	$17.66	3.807%	$18.3323	$18.33	$18.35	$18.30
Purchase #7	$96.73	6.249%	$102.7747	$102.77	$102.75	$102.80
7 purchase totals =	$863.34		$952.3603	$952.36	$952.35	$952.50