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 $85.60   13.740%   $97.3614   $97.36   $97.35   $97.40  
  Purchase #2 $184.54   11.833%   $206.3766   $206.38   $206.40   $206.40  
  Purchase #3 $174.50   13.218%   $197.5654   $197.57   $197.55   $197.60  
  Purchase #4 $153.63   3.290%   $158.6844   $158.68   $158.70   $158.70  
  Purchase #5 $111.92   10.225%   $123.3638   $123.36   $123.35   $123.40  
  Purchase #6 $242.63   7.814%   $261.5891   $261.59   $261.60   $261.60  
  Purchase #7 $79.57   9.129%   $86.8339   $86.83   $86.85   $86.80  
  7 purchase totals = $1,032.39       $1,131.7746   $1,131.77   $1,131.80   $1,131.90