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 $20.68   6.740%   $22.0738   $22.07   $22.05   $22.10  
  Purchase #2 $142.76   12.176%   $160.1425   $160.14   $160.15   $160.10  
  Purchase #3 $139.93   12.318%   $157.1666   $157.17   $157.15   $157.20  
  Purchase #4 $110.71   12.126%   $124.1347   $124.13   $124.15   $124.10  
  Purchase #5 $210.73   6.853%   $225.1713   $225.17   $225.15   $225.20  
  Purchase #6 $36.27   12.677%   $40.8679   $40.87   $40.85   $40.90  
  Purchase #7 $29.32   8.164%   $31.7137   $31.71   $31.70   $31.70  
  7 purchase totals = $690.40       $761.2705   $761.26   $761.20   $761.30