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 $92.36   12.546%   $103.9475   $103.95   $103.95   $103.90  
  Purchase #2 $211.39   4.391%   $220.6721   $220.67   $220.65   $220.70  
  Purchase #3 $60.54   5.149%   $63.6572   $63.66   $63.65   $63.70  
  Purchase #4 $124.56   4.542%   $130.2175   $130.22   $130.20   $130.20  
  Purchase #5 $23.73   10.514%   $26.225   $26.23   $26.25   $26.20  
  Purchase #6 $57.45   7.609%   $61.8214   $61.82   $61.80   $61.80  
  Purchase #7 $240.47   8.117%   $259.9889   $259.99   $260.00   $260.00  
  7 purchase totals = $810.50       $866.5296   $866.54   $866.50   $866.50