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 $70.70   7.771%   $76.1941   $76.19   $76.20   $76.20  
  Purchase #2 $234.63   11.613%   $261.8776   $261.88   $261.90   $261.90  
  Purchase #3 $29.73   11.697%   $33.2075   $33.21   $33.20   $33.20  
  Purchase #4 $141.74   11.369%   $157.8544   $157.85   $157.85   $157.90  
  Purchase #5 $243.87   5.423%   $257.0951   $257.10   $257.10   $257.10  
  Purchase #6 $16.35   11.852%   $18.2878   $18.29   $18.30   $18.30  
  Purchase #7 $89.39   6.725%   $95.4015   $95.40   $95.40   $95.40  
  7 purchase totals = $826.41       $899.9180   $899.92   $899.95   $900.00