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 $217.38   3.435%   $224.847   $224.85   $224.85   $224.80  
  Purchase #2 $123.69   12.139%   $138.7047   $138.70   $138.70   $138.70  
  Purchase #3 $112.37   6.425%   $119.5898   $119.59   $119.60   $119.60  
  Purchase #4 $55.75   10.632%   $61.6773   $61.68   $61.70   $61.70  
  Purchase #5 $133.96   9.275%   $146.3848   $146.38   $146.40   $146.40  
  Purchase #6 $80.95   3.437%   $83.7323   $83.73   $83.75   $83.70  
  Purchase #7 $247.47   3.524%   $256.1908   $256.19   $256.20   $256.20  
  7 purchase totals = $971.57       $1,031.1267   $1,031.12   $1,031.20   $1,031.10