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 $22.86   9.137%   $24.9487   $24.95   $24.95   $24.90  
  Purchase #2 $224.77   9.825%   $246.8537   $246.85   $246.85   $246.90  
  Purchase #3 $250.79   7.604%   $269.8601   $269.86   $269.85   $269.90  
  Purchase #4 $146.31   10.537%   $161.7267   $161.73   $161.75   $161.70  
  Purchase #5 $23.81   9.103%   $25.9774   $25.98   $26.00   $26.00  
  Purchase #6 $83.88   7.371%   $90.0628   $90.06   $90.05   $90.10  
  Purchase #7 $131.70   7.726%   $141.8751   $141.88   $141.90   $141.90  
  7 purchase totals = $884.12       $961.3045   $961.31   $961.35   $961.40