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 $204.77   4.319%   $213.614   $213.61   $213.60   $213.60  
  Purchase #2 $243.92   11.685%   $272.4221   $272.42   $272.40   $272.40  
  Purchase #3 $157.48   13.634%   $178.9508   $178.95   $178.95   $179.00  
  Purchase #4 $211.59   11.354%   $235.6139   $235.61   $235.60   $235.60  
  Purchase #5 $6.33   5.680%   $6.6895   $6.69   $6.70   $6.70  
  Purchase #6 $77.46   5.577%   $81.7799   $81.78   $81.80   $81.80  
  Purchase #7 $119.67   3.237%   $123.5437   $123.54   $123.55   $123.50  
  7 purchase totals = $1,021.22       $1,112.6139   $1,112.60   $1,112.60   $1,112.60