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 $57.84   8.813%   $62.9374   $62.94   $62.95   $62.90  
  Purchase #2 $65.97   12.836%   $74.4379   $74.44   $74.45   $74.40  
  Purchase #3 $165.89   13.747%   $188.6949   $188.69   $188.70   $188.70  
  Purchase #4 $50.42   10.248%   $55.587   $55.59   $55.60   $55.60  
  Purchase #5 $242.60   11.171%   $269.7008   $269.70   $269.70   $269.70  
  Purchase #6 $21.47   9.599%   $23.5309   $23.53   $23.55   $23.50  
  Purchase #7 $26.41   13.232%   $29.9046   $29.90   $29.90   $29.90  
  7 purchase totals = $630.60       $704.7935   $704.79   $704.85   $704.70