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 $25.68   3.802%   $26.6564   $26.66   $26.65   $26.70  
  Purchase #2 $113.50   5.296%   $119.511   $119.51   $119.50   $119.50  
  Purchase #3 $179.95   12.234%   $201.9651   $201.97   $201.95   $202.00  
  Purchase #4 $77.34   9.530%   $84.7105   $84.71   $84.70   $84.70  
  Purchase #5 $61.48   13.857%   $69.9993   $70.00   $70.00   $70.00  
  Purchase #6 $157.94   10.308%   $174.2205   $174.22   $174.20   $174.20  
  Purchase #7 $245.29   12.126%   $275.0339   $275.03   $275.05   $275.00  
  7 purchase totals = $861.18       $952.0967   $952.10   $952.05   $952.10