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	$128.31	7.808%	$138.3284	$138.33	$138.35	$138.30
Purchase #2	$6.81	7.332%	$7.3093	$7.31	$7.30	$7.30
Purchase #3	$187.41	11.796%	$209.5169	$209.52	$209.50	$209.50
Purchase #4	$199.80	13.667%	$227.1067	$227.11	$227.10	$227.10
Purchase #5	$199.74	11.366%	$222.4424	$222.44	$222.45	$222.40
Purchase #6	$157.69	9.236%	$172.2542	$172.25	$172.25	$172.30
Purchase #7	$54.29	10.554%	$60.0198	$60.02	$60.00	$60.00
7 purchase totals =	$934.05		$1,036.9777	$1,036.98	$1,036.95	$1,036.90