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 $233.32   11.635%   $260.4668   $260.47   $260.45   $260.50  
  Purchase #2 $244.59   13.824%   $278.4021   $278.40   $278.40   $278.40  
  Purchase #3 $37.47   4.484%   $39.1502   $39.15   $39.15   $39.20  
  Purchase #4 $114.58   9.531%   $125.5006   $125.50   $125.50   $125.50  
  Purchase #5 $210.53   12.146%   $236.101   $236.10   $236.10   $236.10  
  Purchase #6 $16.48   9.571%   $18.0573   $18.06   $18.05   $18.10  
  Purchase #7 $44.26   9.536%   $48.4806   $48.48   $48.50   $48.50  
  7 purchase totals = $901.23       $1,006.1586   $1,006.16   $1,006.15   $1,006.30