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 $88.48   8.739%   $96.2123   $96.21   $96.20   $96.20  
  Purchase #2 $105.26   13.270%   $119.228   $119.23   $119.25   $119.20  
  Purchase #3 $215.53   9.716%   $236.4709   $236.47   $236.45   $236.50  
  Purchase #4 $65.73   7.454%   $70.6295   $70.63   $70.65   $70.60  
  Purchase #5 $232.57   12.619%   $261.918   $261.92   $261.90   $261.90  
  Purchase #6 $52.90   10.103%   $58.2445   $58.24   $58.25   $58.20  
  Purchase #7 $61.73   4.594%   $64.5659   $64.57   $64.55   $64.60  
  7 purchase totals = $822.20       $907.2691   $907.27   $907.25   $907.20