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	$35.54	4.214%	$37.0377	$37.04	$37.05	$37.00
Purchase #2	$124.76	9.748%	$136.9216	$136.92	$136.90	$136.90
Purchase #3	$34.70	9.407%	$37.9642	$37.96	$37.95	$38.00
Purchase #4	$173.73	13.250%	$196.7492	$196.75	$196.75	$196.70
Purchase #5	$72.86	7.855%	$78.5832	$78.58	$78.60	$78.60
Purchase #6	$88.79	13.184%	$100.4961	$100.50	$100.50	$100.50
Purchase #7	$82.92	10.402%	$91.5453	$91.55	$91.55	$91.50
7 purchase totals =	$613.30		$679.2973	$679.30	$679.30	$679.20