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 $233.96   10.837%   $259.3142   $259.31   $259.30   $259.30  
  Purchase #2 $40.86   13.696%   $46.4562   $46.46   $46.45   $46.50  
  Purchase #3 $22.60   6.404%   $24.0473   $24.05   $24.05   $24.00  
  Purchase #4 $34.98   4.626%   $36.5982   $36.60   $36.60   $36.60  
  Purchase #5 $64.35   4.109%   $66.9941   $66.99   $67.00   $67.00  
  Purchase #6 $240.86   9.473%   $263.6767   $263.68   $263.70   $263.70  
  Purchase #7 $228.38   13.778%   $259.8462   $259.85   $259.85   $259.80  
  7 purchase totals = $865.99       $956.9329   $956.94   $956.95   $956.90