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 $246.87   6.291%   $262.4006   $262.40   $262.40   $262.40  
  Purchase #2 $47.66   4.675%   $49.8881   $49.89   $49.90   $49.90  
  Purchase #3 $165.83   9.455%   $181.5092   $181.51   $181.50   $181.50  
  Purchase #4 $233.90   12.278%   $262.6182   $262.62   $262.60   $262.60  
  Purchase #5 $20.94   5.745%   $22.143   $22.14   $22.15   $22.10  
  Purchase #6 $130.69   4.665%   $136.7867   $136.79   $136.80   $136.80  
  Purchase #7 $31.90   11.574%   $35.5921   $35.59   $35.60   $35.60  
  7 purchase totals = $877.79       $950.9379   $950.94   $950.95   $950.90