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 $81.53   13.664%   $92.6703   $92.67   $92.65   $92.70  
  Purchase #2 $211.27   10.234%   $232.8914   $232.89   $232.90   $232.90  
  Purchase #3 $122.78   6.169%   $130.3543   $130.35   $130.35   $130.40  
  Purchase #4 $137.37   4.553%   $143.6245   $143.62   $143.60   $143.60  
  Purchase #5 $53.32   8.716%   $57.9674   $57.97   $57.95   $58.00  
  Purchase #6 $127.71   10.419%   $141.0161   $141.02   $141.00   $141.00  
  Purchase #7 $175.68   11.725%   $196.2785   $196.28   $196.30   $196.30  
  7 purchase totals = $909.66       $994.8025   $994.80   $994.75   $994.90