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 $67.59   11.514%   $75.3723   $75.37   $75.35   $75.40  
  Purchase #2 $108.63   12.252%   $121.9393   $121.94   $121.95   $121.90  
  Purchase #3 $238.88   12.353%   $268.3888   $268.39   $268.40   $268.40  
  Purchase #4 $102.47   6.602%   $109.2351   $109.24   $109.25   $109.20  
  Purchase #5 $198.48   12.710%   $223.7068   $223.71   $223.70   $223.70  
  Purchase #6 $106.56   12.509%   $119.8896   $119.89   $119.90   $119.90  
  Purchase #7 $174.26   9.719%   $191.1963   $191.20   $191.20   $191.20  
  7 purchase totals = $996.87       $1,109.7282   $1,109.74   $1,109.75   $1,109.70