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 $9.85   9.203%   $10.7565   $10.76   $10.75   $10.80  
  Purchase #2 $7.59   8.290%   $8.2192   $8.22   $8.20   $8.20  
  Purchase #3 $65.99   11.696%   $73.7082   $73.71   $73.70   $73.70  
  Purchase #4 $117.26   8.690%   $127.4499   $127.45   $127.45   $127.40  
  Purchase #5 $126.86   8.702%   $137.8994   $137.90   $137.90   $137.90  
  Purchase #6 $62.68   9.553%   $68.6678   $68.67   $68.65   $68.70  
  Purchase #7 $168.47   6.390%   $179.2352   $179.24   $179.25   $179.20  
  7 purchase totals = $558.70       $605.9362   $605.95   $605.90   $605.90