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 $51.68   13.558%   $58.6868   $58.69   $58.70   $58.70  
  Purchase #2 $128.44   4.246%   $133.8936   $133.89   $133.90   $133.90  
  Purchase #3 $84.78   12.275%   $95.1867   $95.19   $95.20   $95.20  
  Purchase #4 $179.93   7.418%   $193.2772   $193.28   $193.30   $193.30  
  Purchase #5 $66.49   12.638%   $74.893   $74.89   $74.90   $74.90  
  Purchase #6 $129.80   12.454%   $145.9653   $145.97   $145.95   $146.00  
  Purchase #7 $247.91   4.831%   $259.8865   $259.89   $259.90   $259.90  
  7 purchase totals = $889.03       $961.7891   $961.80   $961.85   $961.90