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 $57.86   12.384%   $65.0254   $65.03   $65.05   $65.00  
  Purchase #2 $227.94   6.412%   $242.5555   $242.56   $242.55   $242.60  
  Purchase #3 $105.49   9.147%   $115.1392   $115.14   $115.15   $115.10  
  Purchase #4 $73.46   3.654%   $76.1442   $76.14   $76.15   $76.10  
  Purchase #5 $143.53   13.400%   $162.763   $162.76   $162.75   $162.80  
  Purchase #6 $167.47   5.504%   $176.6875   $176.69   $176.70   $176.70  
  Purchase #7 $183.28   4.570%   $191.6559   $191.66   $191.65   $191.70  
  7 purchase totals = $959.03       $1,029.9707   $1,029.98   $1,030.00   $1,030.00