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 $193.37   5.652%   $204.2993   $204.30   $204.30   $204.30  
  Purchase #2 $216.58   10.227%   $238.7296   $238.73   $238.75   $238.70  
  Purchase #3 $136.70   12.637%   $153.9748   $153.97   $153.95   $154.00  
  Purchase #4 $35.41   5.474%   $37.3483   $37.35   $37.35   $37.30  
  Purchase #5 $224.66   7.857%   $242.3115   $242.31   $242.30   $242.30  
  Purchase #6 $118.25   11.707%   $132.0935   $132.09   $132.10   $132.10  
  Purchase #7 $216.70   9.595%   $237.4924   $237.49   $237.50   $237.50  
  7 purchase totals = $1,141.67       $1,246.2494   $1,246.24   $1,246.25   $1,246.20