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 $118.56   6.309%   $126.04   $126.04   $126.05   $126.00  
  Purchase #2 $53.38   3.788%   $55.402   $55.40   $55.40   $55.40  
  Purchase #3 $138.48   8.615%   $150.4101   $150.41   $150.40   $150.40  
  Purchase #4 $249.39   6.835%   $266.4358   $266.44   $266.45   $266.40  
  Purchase #5 $16.44   3.652%   $17.0404   $17.04   $17.05   $17.00  
  Purchase #6 $85.92   6.170%   $91.2213   $91.22   $91.20   $91.20  
  Purchase #7 $242.94   12.452%   $273.1909   $273.19   $273.20   $273.20  
  7 purchase totals = $905.11       $979.7405   $979.74   $979.75   $979.60