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 $57.66   8.582%   $62.6084   $62.61   $62.60   $62.60  
  Purchase #2 $226.94   12.812%   $256.0156   $256.02   $256.00   $256.00  
  Purchase #3 $76.55   5.209%   $80.5375   $80.54   $80.55   $80.50  
  Purchase #4 $51.90   13.284%   $58.7944   $58.79   $58.80   $58.80  
  Purchase #5 $83.79   4.607%   $87.6502   $87.65   $87.65   $87.70  
  Purchase #6 $94.25   4.749%   $98.7259   $98.73   $98.75   $98.70  
  Purchase #7 $32.57   6.583%   $34.7141   $34.71   $34.70   $34.70  
  7 purchase totals = $623.66       $679.0461   $679.05   $679.05   $679.00