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 $211.71   9.355%   $231.5155   $231.52   $231.50   $231.50  
  Purchase #2 $234.49   11.439%   $261.3133   $261.31   $261.30   $261.30  
  Purchase #3 $77.67   11.845%   $86.87   $86.87   $86.85   $86.90  
  Purchase #4 $152.42   9.157%   $166.3771   $166.38   $166.40   $166.40  
  Purchase #5 $191.69   3.633%   $198.6541   $198.65   $198.65   $198.70  
  Purchase #6 $191.80   7.579%   $206.3365   $206.34   $206.35   $206.30  
  Purchase #7 $88.39   11.599%   $98.6424   $98.64   $98.65   $98.60  
  7 purchase totals = $1,148.17       $1,249.7089   $1,249.71   $1,249.70   $1,249.70