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 $122.63   3.207%   $126.5627   $126.56   $126.55   $126.60  
  Purchase #2 $26.25   8.709%   $28.5361   $28.54   $28.55   $28.50  
  Purchase #3 $51.41   11.514%   $57.3293   $57.33   $57.35   $57.30  
  Purchase #4 $242.86   4.705%   $254.2866   $254.29   $254.30   $254.30  
  Purchase #5 $128.63   10.808%   $142.5323   $142.53   $142.55   $142.50  
  Purchase #6 $16.33   3.378%   $16.8816   $16.88   $16.90   $16.90  
  Purchase #7 $143.55   4.300%   $149.7227   $149.72   $149.70   $149.70  
  7 purchase totals = $731.66       $775.8513   $775.85   $775.90   $775.80