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 $248.61   5.865%   $263.191   $263.19   $263.20   $263.20  
  Purchase #2 $153.28   5.503%   $161.715   $161.72   $161.70   $161.70  
  Purchase #3 $177.93   13.333%   $201.6534   $201.65   $201.65   $201.70  
  Purchase #4 $23.27   3.121%   $23.9963   $24.00   $24.00   $24.00  
  Purchase #5 $15.75   13.386%   $17.8583   $17.86   $17.85   $17.90  
  Purchase #6 $56.49   5.207%   $59.4314   $59.43   $59.45   $59.40  
  Purchase #7 $32.94   3.308%   $34.0297   $34.03   $34.05   $34.00  
  7 purchase totals = $708.27       $761.8751   $761.88   $761.90   $761.90