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 $236.85   10.282%   $261.2029   $261.20   $261.20   $261.20  
  Purchase #2 $158.80   4.724%   $166.3017   $166.30   $166.30   $166.30  
  Purchase #3 $182.91   8.527%   $198.5067   $198.51   $198.50   $198.50  
  Purchase #4 $60.83   6.206%   $64.6051   $64.61   $64.60   $64.60  
  Purchase #5 $37.39   3.637%   $38.7499   $38.75   $38.75   $38.70  
  Purchase #6 $111.96   12.341%   $125.777   $125.78   $125.80   $125.80  
  Purchase #7 $161.43   13.316%   $182.926   $182.93   $182.95   $182.90  
  7 purchase totals = $950.17       $1,038.0693   $1,038.08   $1,038.10   $1,038.00