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 $65.83   9.663%   $72.1912   $72.19   $72.20   $72.20  
  Purchase #2 $181.42   13.747%   $206.3598   $206.36   $206.35   $206.40  
  Purchase #3 $56.61   12.779%   $63.8442   $63.84   $63.85   $63.80  
  Purchase #4 $65.54   12.132%   $73.4913   $73.49   $73.50   $73.50  
  Purchase #5 $233.34   11.602%   $260.4121   $260.41   $260.40   $260.40  
  Purchase #6 $207.39   7.655%   $223.2657   $223.27   $223.25   $223.30  
  Purchase #7 $22.73   8.215%   $24.5973   $24.60   $24.60   $24.60  
  7 purchase totals = $832.86       $924.1616   $924.16   $924.15   $924.20