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	$172.95	9.863%	$190.0081	$190.01	$190.00	$190.00
Purchase #2	$136.90	4.109%	$142.5252	$142.53	$142.55	$142.50
Purchase #3	$247.52	9.161%	$270.1953	$270.20	$270.20	$270.20
Purchase #4	$183.99	8.712%	$200.0192	$200.02	$200.00	$200.00
Purchase #5	$64.89	6.568%	$69.152	$69.15	$69.15	$69.20
Purchase #6	$136.51	10.658%	$151.0592	$151.06	$151.05	$151.10
Purchase #7	$14.49	9.342%	$15.8437	$15.84	$15.85	$15.80
7 purchase totals =	$957.25		$1,038.8027	$1,038.81	$1,038.80	$1,038.80