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 $235.79   11.410%   $262.6936   $262.69   $262.70   $262.70  
  Purchase #2 $6.96   12.771%   $7.8489   $7.85   $7.85   $7.80  
  Purchase #3 $83.25   10.181%   $91.7257   $91.73   $91.75   $91.70  
  Purchase #4 $180.31   12.525%   $202.8938   $202.89   $202.90   $202.90  
  Purchase #5 $42.70   10.744%   $47.2877   $47.29   $47.30   $47.30  
  Purchase #6 $187.91   4.402%   $196.1818   $196.18   $196.20   $196.20  
  Purchase #7 $246.39   5.198%   $259.1974   $259.20   $259.20   $259.20  
  7 purchase totals = $983.31       $1,067.8289   $1,067.83   $1,067.90   $1,067.80