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 $149.79   8.118%   $161.95   $161.95   $161.95   $162.00  
  Purchase #2 $82.25   13.665%   $93.4895   $93.49   $93.50   $93.50  
  Purchase #3 $235.88   5.380%   $248.5703   $248.57   $248.55   $248.60  
  Purchase #4 $151.46   8.242%   $163.9433   $163.94   $163.95   $163.90  
  Purchase #5 $49.47   3.801%   $51.3504   $51.35   $51.35   $51.40  
  Purchase #6 $146.52   8.473%   $158.9346   $158.93   $158.95   $158.90  
  Purchase #7 $176.94   8.200%   $191.4491   $191.45   $191.45   $191.40  
  7 purchase totals = $992.31       $1,069.6872   $1,069.68   $1,069.70   $1,069.70