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 $54.56   13.636%   $61.9998   $62.00   $62.00   $62.00  
  Purchase #2 $100.44   7.514%   $107.9871   $107.99   $108.00   $108.00  
  Purchase #3 $215.25   7.114%   $230.5629   $230.56   $230.55   $230.60  
  Purchase #4 $207.30   4.650%   $216.9395   $216.94   $216.95   $216.90  
  Purchase #5 $73.93   6.551%   $78.7732   $78.77   $78.75   $78.80  
  Purchase #6 $149.71   3.485%   $154.9274   $154.93   $154.95   $154.90  
  Purchase #7 $118.63   10.438%   $131.0126   $131.01   $131.00   $131.00  
  7 purchase totals = $919.82       $982.2025   $982.20   $982.20   $982.20