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 $249.97   7.687%   $269.1852   $269.19   $269.20   $269.20  
  Purchase #2 $32.61   8.203%   $35.285   $35.29   $35.30   $35.30  
  Purchase #3 $170.66   3.481%   $176.6007   $176.60   $176.60   $176.60  
  Purchase #4 $123.87   12.523%   $139.3822   $139.38   $139.40   $139.40  
  Purchase #5 $233.49   12.839%   $263.4678   $263.47   $263.45   $263.50  
  Purchase #6 $55.67   4.808%   $58.3466   $58.35   $58.35   $58.30  
  Purchase #7 $235.82   13.246%   $267.0567   $267.06   $267.05   $267.10  
  7 purchase totals = $1,102.09       $1,209.3242   $1,209.34   $1,209.35   $1,209.40