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 $108.59   9.249%   $118.6335   $118.63   $118.65   $118.60  
  Purchase #2 $75.37   11.537%   $84.0654   $84.07   $84.05   $84.10  
  Purchase #3 $203.70   4.849%   $213.5774   $213.58   $213.60   $213.60  
  Purchase #4 $239.88   6.688%   $255.9232   $255.92   $255.90   $255.90  
  Purchase #5 $167.89   5.292%   $176.7747   $176.77   $176.75   $176.80  
  Purchase #6 $89.49   10.467%   $98.8569   $98.86   $98.85   $98.90  
  Purchase #7 $74.43   5.631%   $78.6212   $78.62   $78.60   $78.60  
  7 purchase totals = $959.35       $1,026.4523   $1,026.45   $1,026.40   $1,026.50