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 $156.62   5.291%   $164.9068   $164.91   $164.90   $164.90  
  Purchase #2 $69.27   5.345%   $72.9725   $72.97   $72.95   $73.00  
  Purchase #3 $165.49   5.153%   $174.0177   $174.02   $174.00   $174.00  
  Purchase #4 $102.76   10.305%   $113.3494   $113.35   $113.35   $113.30  
  Purchase #5 $128.80   6.362%   $136.9943   $136.99   $137.00   $137.00  
  Purchase #6 $177.28   5.311%   $186.6953   $186.70   $186.70   $186.70  
  Purchase #7 $92.44   10.356%   $102.0131   $102.01   $102.00   $102.00  
  7 purchase totals = $892.66       $950.9491   $950.95   $950.90   $950.90