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 $183.61   13.623%   $208.6232   $208.62   $208.60   $208.60  
  Purchase #2 $58.57   3.522%   $60.6328   $60.63   $60.65   $60.60  
  Purchase #3 $57.53   5.508%   $60.6988   $60.70   $60.70   $60.70  
  Purchase #4 $8.27   5.223%   $8.7019   $8.70   $8.70   $8.70  
  Purchase #5 $66.95   8.347%   $72.5383   $72.54   $72.55   $72.50  
  Purchase #6 $199.33   6.199%   $211.6865   $211.69   $211.70   $211.70  
  Purchase #7 $12.85   8.208%   $13.9047   $13.90   $13.90   $13.90  
  7 purchase totals = $587.11       $636.7862   $636.78   $636.80   $636.70