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 $204.48   12.448%   $229.9337   $229.93   $229.95   $229.90  
  Purchase #2 $54.52   12.543%   $61.3584   $61.36   $61.35   $61.40  
  Purchase #3 $65.38   5.872%   $69.2191   $69.22   $69.20   $69.20  
  Purchase #4 $215.65   6.431%   $229.5185   $229.52   $229.50   $229.50  
  Purchase #5 $183.64   13.193%   $207.8676   $207.87   $207.85   $207.90  
  Purchase #6 $240.92   7.695%   $259.4588   $259.46   $259.45   $259.50  
  Purchase #7 $107.71   6.303%   $114.499   $114.50   $114.50   $114.50  
  7 purchase totals = $1,072.30       $1,171.8551   $1,171.86   $1,171.80   $1,171.90