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	$121.81	10.267%	$134.3162	$134.32	$134.30	$134.30
Purchase #2	$168.25	13.613%	$191.1539	$191.15	$191.15	$191.20
Purchase #3	$35.84	11.637%	$40.0107	$40.01	$40.00	$40.00
Purchase #4	$139.84	8.358%	$151.5278	$151.53	$151.55	$151.50
Purchase #5	$21.96	13.494%	$24.9233	$24.92	$24.90	$24.90
Purchase #6	$138.50	9.373%	$151.4816	$151.48	$151.50	$151.50
Purchase #7	$214.41	4.542%	$224.1485	$224.15	$224.15	$224.10
7 purchase totals =	$840.61		$917.5620	$917.56	$917.55	$917.50