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 $23.35   12.134%   $26.1833   $26.18   $26.20   $26.20  
  Purchase #2 $246.58   3.180%   $254.4212   $254.42   $254.40   $254.40  
  Purchase #3 $44.76   7.867%   $48.2813   $48.28   $48.30   $48.30  
  Purchase #4 $71.44   9.713%   $78.379   $78.38   $78.40   $78.40  
  Purchase #5 $117.85   8.560%   $127.938   $127.94   $127.95   $127.90  
  Purchase #6 $35.33   3.173%   $36.451   $36.45   $36.45   $36.50  
  Purchase #7 $248.81   13.466%   $282.3148   $282.31   $282.30   $282.30  
  7 purchase totals = $788.12       $853.9686   $853.96   $854.00   $854.00