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 $46.72   12.609%   $52.6109   $52.61   $52.60   $52.60  
  Purchase #2 $231.26   7.339%   $248.2322   $248.23   $248.25   $248.20  
  Purchase #3 $170.88   10.423%   $188.6908   $188.69   $188.70   $188.70  
  Purchase #4 $160.47   12.719%   $180.8802   $180.88   $180.90   $180.90  
  Purchase #5 $117.85   11.235%   $131.0904   $131.09   $131.10   $131.10  
  Purchase #6 $113.35   11.389%   $126.2594   $126.26   $126.25   $126.30  
  Purchase #7 $112.92   13.386%   $128.0355   $128.04   $128.05   $128.00  
  7 purchase totals = $953.45       $1,055.7994   $1,055.80   $1,055.85   $1,055.80