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 $56.68   5.213%   $59.6347   $59.63   $59.65   $59.60  
  Purchase #2 $111.73   11.549%   $124.6337   $124.63   $124.65   $124.60  
  Purchase #3 $95.40   7.409%   $102.4682   $102.47   $102.45   $102.50  
  Purchase #4 $175.30   7.721%   $188.8349   $188.83   $188.85   $188.80  
  Purchase #5 $228.58   4.705%   $239.3347   $239.33   $239.35   $239.30  
  Purchase #6 $246.44   12.105%   $276.2716   $276.27   $276.25   $276.30  
  Purchase #7 $227.48   5.264%   $239.4545   $239.45   $239.45   $239.50  
  7 purchase totals = $1,141.61       $1,230.6323   $1,230.61   $1,230.65   $1,230.60