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 $208.77   8.586%   $226.695   $226.70   $226.70   $226.70  
  Purchase #2 $19.95   6.398%   $21.2264   $21.23   $21.25   $21.20  
  Purchase #3 $164.79   12.170%   $184.8449   $184.84   $184.85   $184.80  
  Purchase #4 $143.97   7.127%   $154.2307   $154.23   $154.25   $154.20  
  Purchase #5 $25.54   4.153%   $26.6007   $26.60   $26.60   $26.60  
  Purchase #6 $124.72   5.601%   $131.7056   $131.71   $131.70   $131.70  
  Purchase #7 $76.33   10.730%   $84.5202   $84.52   $84.50   $84.50  
  7 purchase totals = $764.07       $829.8235   $829.83   $829.85   $829.70