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 $204.69   13.847%   $233.0334   $233.03   $233.05   $233.00  
  Purchase #2 $125.65   12.313%   $141.1213   $141.12   $141.10   $141.10  
  Purchase #3 $208.92   10.154%   $230.1337   $230.13   $230.15   $230.10  
  Purchase #4 $44.40   6.462%   $47.2691   $47.27   $47.25   $47.30  
  Purchase #5 $38.40   10.853%   $42.5676   $42.57   $42.55   $42.60  
  Purchase #6 $74.99   5.705%   $79.2682   $79.27   $79.25   $79.30  
  Purchase #7 $36.66   7.635%   $39.459   $39.46   $39.45   $39.50  
  7 purchase totals = $733.71       $812.8523   $812.85   $812.80   $812.90