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 $23.87   10.527%   $26.3828   $26.38   $26.40   $26.40  
  Purchase #2 $145.88   13.808%   $166.0231   $166.02   $166.00   $166.00  
  Purchase #3 $63.81   6.131%   $67.7222   $67.72   $67.70   $67.70  
  Purchase #4 $206.86   9.439%   $226.3855   $226.39   $226.40   $226.40  
  Purchase #5 $76.45   13.585%   $86.8357   $86.84   $86.85   $86.80  
  Purchase #6 $174.98   3.681%   $181.421   $181.42   $181.40   $181.40  
  Purchase #7 $174.44   10.684%   $193.0772   $193.08   $193.10   $193.10  
  7 purchase totals = $866.29       $947.8475   $947.85   $947.85   $947.80