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 $130.40   8.326%   $141.2571   $141.26   $141.25   $141.30  
  Purchase #2 $63.88   3.295%   $65.9848   $65.98   $66.00   $66.00  
  Purchase #3 $93.80   9.311%   $102.5337   $102.53   $102.55   $102.50  
  Purchase #4 $188.54   12.196%   $211.5343   $211.53   $211.55   $211.50  
  Purchase #5 $31.63   7.308%   $33.9415   $33.94   $33.95   $33.90  
  Purchase #6 $129.27   11.345%   $143.9357   $143.94   $143.95   $143.90  
  Purchase #7 $44.86   4.576%   $46.9128   $46.91   $46.90   $46.90  
  7 purchase totals = $682.38       $746.0999   $746.09   $746.15   $746.00