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 $221.71   8.811%   $241.2449   $241.24   $241.25   $241.20  
  Purchase #2 $23.95   12.143%   $26.8582   $26.86   $26.85   $26.90  
  Purchase #3 $175.60   5.154%   $184.6504   $184.65   $184.65   $184.70  
  Purchase #4 $88.44   8.243%   $95.7301   $95.73   $95.75   $95.70  
  Purchase #5 $186.66   12.295%   $209.6098   $209.61   $209.60   $209.60  
  Purchase #6 $154.46   6.657%   $164.7424   $164.74   $164.75   $164.70  
  Purchase #7 $29.57   9.844%   $32.4809   $32.48   $32.50   $32.50  
  7 purchase totals = $880.39       $955.3167   $955.31   $955.35   $955.30