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 $60.91   4.650%   $63.7423   $63.74   $63.75   $63.70  
  Purchase #2 $216.60   11.216%   $240.8939   $240.89   $240.90   $240.90  
  Purchase #3 $51.42   12.382%   $57.7868   $57.79   $57.80   $57.80  
  Purchase #4 $233.52   5.338%   $245.9853   $245.99   $246.00   $246.00  
  Purchase #5 $90.62   6.141%   $96.185   $96.19   $96.20   $96.20  
  Purchase #6 $123.58   3.425%   $127.8126   $127.81   $127.80   $127.80  
  Purchase #7 $126.28   13.660%   $143.5298   $143.53   $143.55   $143.50  
  7 purchase totals = $902.93       $975.9357   $975.94   $976.00   $975.90