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 $51.90   12.249%   $58.2572   $58.26   $58.25   $58.30  
  Purchase #2 $242.64   11.271%   $269.988   $269.99   $270.00   $270.00  
  Purchase #3 $189.81   6.123%   $201.4321   $201.43   $201.45   $201.40  
  Purchase #4 $176.52   10.855%   $195.6812   $195.68   $195.70   $195.70  
  Purchase #5 $133.52   4.134%   $139.0397   $139.04   $139.05   $139.00  
  Purchase #6 $227.40   13.269%   $257.5737   $257.57   $257.55   $257.60  
  Purchase #7 $98.93   13.174%   $111.963   $111.96   $111.95   $112.00  
  7 purchase totals = $1,120.72       $1,233.9349   $1,233.93   $1,233.95   $1,234.00