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 $208.97   8.275%   $226.2623   $226.26   $226.25   $226.30  
  Purchase #2 $120.31   4.186%   $125.3462   $125.35   $125.35   $125.30  
  Purchase #3 $94.66   7.181%   $101.4575   $101.46   $101.45   $101.50  
  Purchase #4 $78.50   3.153%   $80.9751   $80.98   $81.00   $81.00  
  Purchase #5 $60.83   7.517%   $65.4026   $65.40   $65.40   $65.40  
  Purchase #6 $33.30   7.724%   $35.8721   $35.87   $35.85   $35.90  
  Purchase #7 $205.62   8.435%   $222.964   $222.96   $222.95   $223.00  
  7 purchase totals = $802.19       $858.2798   $858.28   $858.25   $858.40