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 $85.94   10.701%   $95.1364   $95.14   $95.15   $95.10  
  Purchase #2 $182.64   11.179%   $203.0573   $203.06   $203.05   $203.10  
  Purchase #3 $25.70   4.853%   $26.9472   $26.95   $26.95   $26.90  
  Purchase #4 $227.48   12.333%   $255.5351   $255.54   $255.55   $255.50  
  Purchase #5 $127.85   3.255%   $132.0115   $132.01   $132.00   $132.00  
  Purchase #6 $30.71   13.433%   $34.8353   $34.84   $34.85   $34.80  
  Purchase #7 $125.81   12.858%   $141.9866   $141.99   $142.00   $142.00  
  7 purchase totals = $806.13       $889.5094   $889.53   $889.55   $889.40