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 $34.26   3.116%   $35.3275   $35.33   $35.35   $35.30  
  Purchase #2 $63.57   6.743%   $67.8565   $67.86   $67.85   $67.90  
  Purchase #3 $154.76   5.299%   $162.9607   $162.96   $162.95   $163.00  
  Purchase #4 $16.46   13.223%   $18.6365   $18.64   $18.65   $18.60  
  Purchase #5 $236.97   5.618%   $250.283   $250.28   $250.30   $250.30  
  Purchase #6 $125.35   7.428%   $134.661   $134.66   $134.65   $134.70  
  Purchase #7 $41.34   6.306%   $43.9469   $43.95   $43.95   $43.90  
  7 purchase totals = $672.71       $713.6721   $713.68   $713.70   $713.70