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 $58.52   8.438%   $63.4579   $63.46   $63.45   $63.50  
  Purchase #2 $219.48   12.622%   $247.1828   $247.18   $247.20   $247.20  
  Purchase #3 $9.78   12.223%   $10.9754   $10.98   $11.00   $11.00  
  Purchase #4 $176.25   13.355%   $199.7882   $199.79   $199.80   $199.80  
  Purchase #5 $224.42   10.366%   $247.6834   $247.68   $247.70   $247.70  
  Purchase #6 $118.66   10.622%   $131.2641   $131.26   $131.25   $131.30  
  Purchase #7 $32.43   10.291%   $35.7674   $35.77   $35.75   $35.80  
  7 purchase totals = $839.54       $936.1192   $936.12   $936.15   $936.30