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 $236.82   6.377%   $251.922   $251.92   $251.90   $251.90  
  Purchase #2 $48.87   3.818%   $50.7359   $50.74   $50.75   $50.70  
  Purchase #3 $64.26   5.675%   $67.9068   $67.91   $67.90   $67.90  
  Purchase #4 $173.26   8.418%   $187.845   $187.85   $187.85   $187.80  
  Purchase #5 $227.75   13.863%   $259.323   $259.32   $259.30   $259.30  
  Purchase #6 $118.94   8.725%   $129.3175   $129.32   $129.30   $129.30  
  Purchase #7 $124.44   9.608%   $136.3962   $136.40   $136.40   $136.40  
  7 purchase totals = $994.34       $1,083.4464   $1,083.46   $1,083.40   $1,083.30