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 $58.44   4.207%   $60.8986   $60.90   $60.90   $60.90  
  Purchase #2 $49.63   11.531%   $55.3528   $55.35   $55.35   $55.40  
  Purchase #3 $25.55   10.577%   $28.2524   $28.25   $28.25   $28.30  
  Purchase #4 $230.57   8.157%   $249.3776   $249.38   $249.40   $249.40  
  Purchase #5 $6.79   4.772%   $7.114   $7.11   $7.10   $7.10  
  Purchase #6 $158.64   11.399%   $176.7234   $176.72   $176.70   $176.70  
  Purchase #7 $239.74   7.589%   $257.9339   $257.93   $257.95   $257.90  
  7 purchase totals = $769.36       $835.6527   $835.64   $835.65   $835.70