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 $46.83   10.209%   $51.6109   $51.61   $51.60   $51.60  
  Purchase #2 $76.94   5.791%   $81.3956   $81.40   $81.40   $81.40  
  Purchase #3 $213.26   12.511%   $239.941   $239.94   $239.95   $239.90  
  Purchase #4 $45.85   4.377%   $47.8569   $47.86   $47.85   $47.90  
  Purchase #5 $133.93   5.437%   $141.2118   $141.21   $141.20   $141.20  
  Purchase #6 $183.63   3.659%   $190.349   $190.35   $190.35   $190.30  
  Purchase #7 $204.32   7.452%   $219.5459   $219.55   $219.55   $219.50  
  7 purchase totals = $904.76       $971.9111   $971.92   $971.90   $971.80