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 $79.66   11.665%   $88.9523   $88.95   $88.95   $89.00  
  Purchase #2 $248.47   5.311%   $261.6662   $261.67   $261.65   $261.70  
  Purchase #3 $23.84   5.578%   $25.1698   $25.17   $25.15   $25.20  
  Purchase #4 $89.62   7.782%   $96.5942   $96.59   $96.60   $96.60  
  Purchase #5 $70.48   5.614%   $74.4367   $74.44   $74.45   $74.40  
  Purchase #6 $87.45   10.540%   $96.6672   $96.67   $96.65   $96.70  
  Purchase #7 $93.42   8.206%   $101.086   $101.09   $101.10   $101.10  
  7 purchase totals = $692.94       $744.5724   $744.58   $744.55   $744.70