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 $68.81   10.844%   $76.2718   $76.27   $76.25   $76.30  
  Purchase #2 $111.92   6.561%   $119.2631   $119.26   $119.25   $119.30  
  Purchase #3 $113.70   3.680%   $117.8842   $117.88   $117.90   $117.90  
  Purchase #4 $53.87   12.626%   $60.6716   $60.67   $60.65   $60.70  
  Purchase #5 $64.92   5.850%   $68.7178   $68.72   $68.70   $68.70  
  Purchase #6 $228.72   9.720%   $250.9516   $250.95   $250.95   $251.00  
  Purchase #7 $243.86   9.301%   $266.5414   $266.54   $266.55   $266.50  
  7 purchase totals = $885.80       $960.3015   $960.29   $960.25   $960.40