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 $8.95   11.610%   $9.9891   $9.99   $10.00   $10.00  
  Purchase #2 $246.89   4.269%   $257.4297   $257.43   $257.45   $257.40  
  Purchase #3 $199.62   5.286%   $210.1719   $210.17   $210.15   $210.20  
  Purchase #4 $20.45   10.612%   $22.6202   $22.62   $22.60   $22.60  
  Purchase #5 $13.94   6.747%   $14.8805   $14.88   $14.90   $14.90  
  Purchase #6 $186.78   4.719%   $195.5941   $195.59   $195.60   $195.60  
  Purchase #7 $97.61   7.108%   $104.5481   $104.55   $104.55   $104.50  
  7 purchase totals = $774.24       $815.2336   $815.23   $815.25   $815.20