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 $53.41   5.859%   $56.5393   $56.54   $56.55   $56.50  
  Purchase #2 $199.41   13.455%   $226.2406   $226.24   $226.25   $226.20  
  Purchase #3 $22.67   4.288%   $23.6421   $23.64   $23.65   $23.60  
  Purchase #4 $47.86   3.132%   $49.359   $49.36   $49.35   $49.40  
  Purchase #5 $248.57   3.346%   $256.8872   $256.89   $256.90   $256.90  
  Purchase #6 $103.67   6.338%   $110.2406   $110.24   $110.25   $110.20  
  Purchase #7 $14.32   7.824%   $15.4404   $15.44   $15.45   $15.40  
  7 purchase totals = $689.91       $738.3492   $738.35   $738.40   $738.20