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	$93.81	7.131%	$100.4996	$100.50	$100.50	$100.50
Purchase #2	$82.34	6.381%	$87.5941	$87.59	$87.60	$87.60
Purchase #3	$25.76	9.239%	$28.14	$28.14	$28.15	$28.10
Purchase #4	$89.35	8.409%	$96.8634	$96.86	$96.85	$96.90
Purchase #5	$169.96	3.521%	$175.9443	$175.94	$175.95	$175.90
Purchase #6	$133.31	7.169%	$142.867	$142.87	$142.85	$142.90
Purchase #7	$66.85	10.550%	$73.9027	$73.90	$73.90	$73.90
7 purchase totals =	$661.38		$705.8111	$705.80	$705.80	$705.80