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 $64.92   13.801%   $73.8796   $73.88   $73.90   $73.90  
  Purchase #2 $176.77   13.563%   $200.7453   $200.75   $200.75   $200.70  
  Purchase #3 $14.89   13.499%   $16.9   $16.90   $16.90   $16.90  
  Purchase #4 $86.50   13.604%   $98.2675   $98.27   $98.25   $98.30  
  Purchase #5 $89.65   8.611%   $97.3698   $97.37   $97.35   $97.40  
  Purchase #6 $193.36   8.574%   $209.9387   $209.94   $209.95   $209.90  
  Purchase #7 $69.59   7.608%   $74.8844   $74.88   $74.90   $74.90  
  7 purchase totals = $695.68       $771.9853   $771.99   $772.00   $772.00