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 $85.94   8.697%   $93.4142   $93.41   $93.40   $93.40  
  Purchase #2 $28.54   9.463%   $31.2407   $31.24   $31.25   $31.20  
  Purchase #3 $245.78   8.195%   $265.9217   $265.92   $265.90   $265.90  
  Purchase #4 $23.94   10.703%   $26.5023   $26.50   $26.50   $26.50  
  Purchase #5 $219.39   4.224%   $228.657   $228.66   $228.65   $228.70  
  Purchase #6 $190.66   9.102%   $208.0139   $208.01   $208.00   $208.00  
  Purchase #7 $114.69   7.616%   $123.4248   $123.42   $123.40   $123.40  
  7 purchase totals = $908.94       $977.1746   $977.16   $977.10   $977.10