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	$89.35	12.469%	$100.4911	$100.49	$100.50	$100.50
Purchase #2	$94.39	10.317%	$104.1282	$104.13	$104.15	$104.10
Purchase #3	$161.60	9.770%	$177.3883	$177.39	$177.40	$177.40
Purchase #4	$218.35	5.116%	$229.5208	$229.52	$229.50	$229.50
Purchase #5	$12.45	13.796%	$14.1676	$14.17	$14.15	$14.20
Purchase #6	$31.46	4.776%	$32.9625	$32.96	$32.95	$33.00
Purchase #7	$222.34	11.646%	$248.2337	$248.23	$248.25	$248.20
7 purchase totals =	$829.94		$906.8922	$906.89	$906.90	$906.90