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 $235.98   10.615%   $261.0293   $261.03   $261.05   $261.00  
  Purchase #2 $156.55   12.222%   $175.6835   $175.68   $175.70   $175.70  
  Purchase #3 $155.86   13.106%   $176.287   $176.29   $176.30   $176.30  
  Purchase #4 $54.70   3.712%   $56.7305   $56.73   $56.75   $56.70  
  Purchase #5 $37.56   6.112%   $39.8557   $39.86   $39.85   $39.90  
  Purchase #6 $213.84   7.383%   $229.6278   $229.63   $229.65   $229.60  
  Purchase #7 $64.34   12.166%   $72.1676   $72.17   $72.15   $72.20  
  7 purchase totals = $918.83       $1,011.3814   $1,011.39   $1,011.45   $1,011.40