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 $109.67   8.653%   $119.1597   $119.16   $119.15   $119.20  
  Purchase #2 $16.34   8.237%   $17.6859   $17.69   $17.70   $17.70  
  Purchase #3 $235.31   5.753%   $248.8474   $248.85   $248.85   $248.80  
  Purchase #4 $118.48   7.639%   $127.5307   $127.53   $127.55   $127.50  
  Purchase #5 $8.30   4.489%   $8.6726   $8.67   $8.65   $8.70  
  Purchase #6 $43.87   4.158%   $45.6941   $45.69   $45.70   $45.70  
  Purchase #7 $78.60   6.756%   $83.9102   $83.91   $83.90   $83.90  
  7 purchase totals = $610.57       $651.5006   $651.50   $651.50   $651.50