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 $182.39   11.745%   $203.8117   $203.81   $203.80   $203.80  
  Purchase #2 $59.92   4.493%   $62.6122   $62.61   $62.60   $62.60  
  Purchase #3 $190.26   4.154%   $198.1634   $198.16   $198.15   $198.20  
  Purchase #4 $27.89   7.399%   $29.9536   $29.95   $29.95   $30.00  
  Purchase #5 $60.46   4.439%   $63.1438   $63.14   $63.15   $63.10  
  Purchase #6 $16.51   5.197%   $17.368   $17.37   $17.35   $17.40  
  Purchase #7 $178.56   13.868%   $203.3227   $203.32   $203.30   $203.30  
  7 purchase totals = $715.99       $778.3754   $778.36   $778.30   $778.40