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	$21.44	6.785%	$22.8947	$22.89	$22.90	$22.90
Purchase #2	$144.59	11.708%	$161.5186	$161.52	$161.50	$161.50
Purchase #3	$137.56	10.442%	$151.924	$151.92	$151.90	$151.90
Purchase #4	$216.84	4.496%	$226.5891	$226.59	$226.60	$226.60
Purchase #5	$124.76	10.573%	$137.9509	$137.95	$137.95	$138.00
Purchase #6	$119.79	3.483%	$123.9623	$123.96	$123.95	$124.00
Purchase #7	$82.29	4.240%	$85.7791	$85.78	$85.80	$85.80
7 purchase totals =	$847.27		$910.6187	$910.61	$910.60	$910.70