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	$153.53	9.584%	$168.2443	$168.24	$168.25	$168.20
Purchase #2	$153.68	11.428%	$171.2426	$171.24	$171.25	$171.20
Purchase #3	$75.78	10.799%	$83.9635	$83.96	$83.95	$84.00
Purchase #4	$200.94	11.640%	$224.3294	$224.33	$224.35	$224.30
Purchase #5	$247.50	10.111%	$272.5247	$272.52	$272.50	$272.50
Purchase #6	$246.71	12.813%	$278.321	$278.32	$278.30	$278.30
Purchase #7	$116.93	5.429%	$123.2781	$123.28	$123.30	$123.30
7 purchase totals =	$1,195.07		$1,321.9036	$1,321.89	$1,321.90	$1,321.80