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 $110.49   10.452%   $122.0384   $122.04   $122.05   $122.00  
  Purchase #2 $82.83   13.538%   $94.0435   $94.04   $94.05   $94.00  
  Purchase #3 $186.50   12.507%   $209.8256   $209.83   $209.85   $209.80  
  Purchase #4 $86.76   10.217%   $95.6243   $95.62   $95.60   $95.60  
  Purchase #5 $29.67   12.788%   $33.4642   $33.46   $33.45   $33.50  
  Purchase #6 $66.83   8.360%   $72.417   $72.42   $72.40   $72.40  
  Purchase #7 $177.81   13.754%   $202.266   $202.27   $202.25   $202.30  
  7 purchase totals = $740.89       $829.6790   $829.68   $829.65   $829.60