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 $104.82   13.872%   $119.3606   $119.36   $119.35   $119.40  
  Purchase #2 $108.91   11.525%   $121.4619   $121.46   $121.45   $121.50  
  Purchase #3 $80.64   9.194%   $88.054   $88.05   $88.05   $88.10  
  Purchase #4 $55.30   4.352%   $57.7067   $57.71   $57.70   $57.70  
  Purchase #5 $126.33   7.860%   $136.2595   $136.26   $136.25   $136.30  
  Purchase #6 $176.67   12.671%   $199.0559   $199.06   $199.05   $199.10  
  Purchase #7 $238.76   8.873%   $259.9452   $259.95   $259.95   $259.90  
  7 purchase totals = $891.43       $981.8438   $981.85   $981.80   $982.00