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 $243.88   11.402%   $271.6872   $271.69   $271.70   $271.70  
  Purchase #2 $62.46   8.861%   $67.9946   $67.99   $68.00   $68.00  
  Purchase #3 $234.44   13.459%   $265.9933   $265.99   $266.00   $266.00  
  Purchase #4 $6.82   4.116%   $7.1007   $7.10   $7.10   $7.10  
  Purchase #5 $60.26   10.526%   $66.603   $66.60   $66.60   $66.60  
  Purchase #6 $243.42   7.594%   $261.9053   $261.91   $261.90   $261.90  
  Purchase #7 $238.56   9.645%   $261.5691   $261.57   $261.55   $261.60  
  7 purchase totals = $1,089.84       $1,202.8532   $1,202.85   $1,202.85   $1,202.90