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 $235.71   11.221%   $262.159   $262.16   $262.15   $262.20  
  Purchase #2 $18.58   6.381%   $19.7656   $19.77   $19.75   $19.80  
  Purchase #3 $76.89   6.119%   $81.5949   $81.59   $81.60   $81.60  
  Purchase #4 $225.38   11.109%   $250.4175   $250.42   $250.40   $250.40  
  Purchase #5 $9.41   7.272%   $10.0943   $10.09   $10.10   $10.10  
  Purchase #6 $163.30   12.199%   $183.221   $183.22   $183.20   $183.20  
  Purchase #7 $130.95   9.325%   $143.1611   $143.16   $143.15   $143.20  
  7 purchase totals = $860.22       $950.4134   $950.41   $950.35   $950.50