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 $64.60   7.198%   $69.2499   $69.25   $69.25   $69.20  
  Purchase #2 $125.78   10.271%   $138.6989   $138.70   $138.70   $138.70  
  Purchase #3 $17.74   6.308%   $18.859   $18.86   $18.85   $18.90  
  Purchase #4 $198.33   4.842%   $207.9331   $207.93   $207.95   $207.90  
  Purchase #5 $223.44   6.343%   $237.6128   $237.61   $237.60   $237.60  
  Purchase #6 $236.93   5.417%   $249.7645   $249.76   $249.75   $249.80  
  Purchase #7 $116.48   3.789%   $120.8934   $120.89   $120.90   $120.90  
  7 purchase totals = $983.30       $1,043.0116   $1,043.00   $1,043.00   $1,043.00