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 $217.49   9.568%   $238.2994   $238.30   $238.30   $238.30  
  Purchase #2 $96.36   9.619%   $105.6289   $105.63   $105.65   $105.60  
  Purchase #3 $46.58   8.401%   $50.4932   $50.49   $50.50   $50.50  
  Purchase #4 $154.62   12.270%   $173.5919   $173.59   $173.60   $173.60  
  Purchase #5 $85.25   10.739%   $94.405   $94.41   $94.40   $94.40  
  Purchase #6 $107.27   4.423%   $112.0146   $112.01   $112.00   $112.00  
  Purchase #7 $140.50   9.267%   $153.5201   $153.52   $153.50   $153.50  
  7 purchase totals = $848.07       $927.9531   $927.95   $927.95   $927.90