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 $66.67   13.619%   $75.7498   $75.75   $75.75   $75.70  
  Purchase #2 $179.31   13.576%   $203.6531   $203.65   $203.65   $203.70  
  Purchase #3 $11.86   11.138%   $13.181   $13.18   $13.20   $13.20  
  Purchase #4 $224.59   9.811%   $246.6245   $246.62   $246.60   $246.60  
  Purchase #5 $96.88   7.743%   $104.3814   $104.38   $104.40   $104.40  
  Purchase #6 $91.73   11.594%   $102.3652   $102.37   $102.35   $102.40  
  Purchase #7 $164.47   8.641%   $178.6819   $178.68   $178.70   $178.70  
  7 purchase totals = $835.51       $924.6369   $924.63   $924.65   $924.70