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 $53.48   13.282%   $60.5832   $60.58   $60.60   $60.60  
  Purchase #2 $157.85   11.266%   $175.6334   $175.63   $175.65   $175.60  
  Purchase #3 $51.53   11.551%   $57.4822   $57.48   $57.50   $57.50  
  Purchase #4 $49.84   6.182%   $52.9211   $52.92   $52.90   $52.90  
  Purchase #5 $110.76   13.699%   $125.933   $125.93   $125.95   $125.90  
  Purchase #6 $69.48   12.174%   $77.9385   $77.94   $77.95   $77.90  
  Purchase #7 $116.82   7.604%   $125.703   $125.70   $125.70   $125.70  
  7 purchase totals = $609.76       $676.1944   $676.18   $676.25   $676.10