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 $21.59   11.808%   $24.1393   $24.14   $24.15   $24.10  
  Purchase #2 $180.46   8.198%   $195.2541   $195.25   $195.25   $195.30  
  Purchase #3 $91.73   11.822%   $102.5743   $102.57   $102.55   $102.60  
  Purchase #4 $237.60   6.731%   $253.5929   $253.59   $253.60   $253.60  
  Purchase #5 $51.92   9.264%   $56.7299   $56.73   $56.75   $56.70  
  Purchase #6 $204.87   10.469%   $226.3178   $226.32   $226.30   $226.30  
  Purchase #7 $185.86   12.540%   $209.1668   $209.17   $209.15   $209.20  
  7 purchase totals = $974.03       $1,067.7751   $1,067.77   $1,067.75   $1,067.80