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 $148.27   11.102%   $164.7309   $164.73   $164.75   $164.70  
  Purchase #2 $45.96   11.531%   $51.2596   $51.26   $51.25   $51.30  
  Purchase #3 $119.31   3.723%   $123.7519   $123.75   $123.75   $123.80  
  Purchase #4 $66.26   11.259%   $73.7202   $73.72   $73.70   $73.70  
  Purchase #5 $50.26   8.605%   $54.5849   $54.58   $54.60   $54.60  
  Purchase #6 $22.36   3.341%   $23.107   $23.11   $23.10   $23.10  
  Purchase #7 $131.92   3.594%   $136.6612   $136.66   $136.65   $136.70  
  7 purchase totals = $584.34       $627.8157   $627.81   $627.80   $627.90