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 $95.27   8.725%   $103.5823   $103.58   $103.60   $103.60  
  Purchase #2 $205.53   7.548%   $221.0434   $221.04   $221.05   $221.00  
  Purchase #3 $110.44   3.445%   $114.2447   $114.24   $114.25   $114.20  
  Purchase #4 $237.60   8.831%   $258.5825   $258.58   $258.60   $258.60  
  Purchase #5 $35.89   6.617%   $38.2648   $38.26   $38.25   $38.30  
  Purchase #6 $102.27   5.204%   $107.5921   $107.59   $107.60   $107.60  
  Purchase #7 $61.36   3.474%   $63.4916   $63.49   $63.50   $63.50  
  7 purchase totals = $848.36       $906.8014   $906.78   $906.85   $906.80