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 $195.93   7.763%   $211.14   $211.14   $211.15   $211.10  
  Purchase #2 $76.84   9.112%   $83.8417   $83.84   $83.85   $83.80  
  Purchase #3 $21.95   5.480%   $23.1529   $23.15   $23.15   $23.20  
  Purchase #4 $250.37   9.358%   $273.7996   $273.80   $273.80   $273.80  
  Purchase #5 $9.29   5.662%   $9.816   $9.82   $9.80   $9.80  
  Purchase #6 $137.69   4.332%   $143.6547   $143.65   $143.65   $143.70  
  Purchase #7 $24.99   11.380%   $27.8339   $27.83   $27.85   $27.80  
  7 purchase totals = $717.06       $773.2388   $773.23   $773.25   $773.20