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 $221.59   6.524%   $236.0465   $236.05   $236.05   $236.00  
  Purchase #2 $159.34   4.593%   $166.6585   $166.66   $166.65   $166.70  
  Purchase #3 $136.78   7.186%   $146.609   $146.61   $146.60   $146.60  
  Purchase #4 $47.35   3.207%   $48.8685   $48.87   $48.85   $48.90  
  Purchase #5 $228.61   12.844%   $257.9727   $257.97   $257.95   $258.00  
  Purchase #6 $87.78   6.818%   $93.7648   $93.76   $93.75   $93.80  
  Purchase #7 $12.59   9.471%   $13.7824   $13.78   $13.80   $13.80  
  7 purchase totals = $894.04       $963.7024   $963.70   $963.65   $963.80