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 $241.50   8.102%   $261.0663   $261.07   $261.05   $261.10  
  Purchase #2 $245.87   7.855%   $265.1831   $265.18   $265.20   $265.20  
  Purchase #3 $58.59   10.367%   $64.664   $64.66   $64.65   $64.70  
  Purchase #4 $202.99   7.339%   $217.8874   $217.89   $217.90   $217.90  
  Purchase #5 $183.35   12.780%   $206.7821   $206.78   $206.80   $206.80  
  Purchase #6 $8.90   11.270%   $9.903   $9.90   $9.90   $9.90  
  Purchase #7 $47.54   3.690%   $49.2942   $49.29   $49.30   $49.30  
  7 purchase totals = $988.74       $1,074.7801   $1,074.77   $1,074.80   $1,074.90