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 $214.94   8.445%   $233.0917   $233.09   $233.10   $233.10  
  Purchase #2 $249.47   10.459%   $275.5621   $275.56   $275.55   $275.60  
  Purchase #3 $22.71   10.844%   $25.1727   $25.17   $25.15   $25.20  
  Purchase #4 $103.86   9.193%   $113.4078   $113.41   $113.40   $113.40  
  Purchase #5 $60.92   6.591%   $64.9352   $64.94   $64.95   $64.90  
  Purchase #6 $138.44   5.748%   $146.3975   $146.40   $146.40   $146.40  
  Purchase #7 $68.93   12.172%   $77.3202   $77.32   $77.30   $77.30  
  7 purchase totals = $859.27       $935.8872   $935.89   $935.85   $935.90