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 $150.56   4.398%   $157.1816   $157.18   $157.20   $157.20  
  Purchase #2 $122.92   3.236%   $126.8977   $126.90   $126.90   $126.90  
  Purchase #3 $105.40   13.502%   $119.6311   $119.63   $119.65   $119.60  
  Purchase #4 $97.39   7.281%   $104.481   $104.48   $104.50   $104.50  
  Purchase #5 $113.38   9.564%   $124.2237   $124.22   $124.20   $124.20  
  Purchase #6 $228.59   10.484%   $252.5554   $252.56   $252.55   $252.60  
  Purchase #7 $125.92   12.269%   $141.3691   $141.37   $141.35   $141.40  
  7 purchase totals = $944.16       $1,026.3396   $1,026.34   $1,026.35   $1,026.40