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 $57.74   6.210%   $61.3257   $61.33   $61.35   $61.30  
  Purchase #2 $102.97   10.347%   $113.6243   $113.62   $113.60   $113.60  
  Purchase #3 $206.74   9.790%   $226.9798   $226.98   $227.00   $227.00  
  Purchase #4 $144.69   7.817%   $156.0004   $156.00   $156.00   $156.00  
  Purchase #5 $65.88   5.762%   $69.676   $69.68   $69.70   $69.70  
  Purchase #6 $230.99   6.432%   $245.8473   $245.85   $245.85   $245.80  
  Purchase #7 $22.59   4.246%   $23.5492   $23.55   $23.55   $23.50  
  7 purchase totals = $831.60       $897.0027   $897.01   $897.05   $896.90