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 $43.72   8.857%   $47.5923   $47.59   $47.60   $47.60  
  Purchase #2 $234.72   10.621%   $259.6496   $259.65   $259.65   $259.60  
  Purchase #3 $171.62   3.351%   $177.371   $177.37   $177.35   $177.40  
  Purchase #4 $25.70   3.538%   $26.6093   $26.61   $26.60   $26.60  
  Purchase #5 $159.45   12.818%   $179.8883   $179.89   $179.90   $179.90  
  Purchase #6 $137.79   3.425%   $142.5093   $142.51   $142.50   $142.50  
  Purchase #7 $94.76   12.538%   $106.641   $106.64   $106.65   $106.60  
  7 purchase totals = $867.76       $940.2608   $940.26   $940.25   $940.20