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 $83.59   12.697%   $94.2034   $94.20   $94.20   $94.20  
  Purchase #2 $122.58   11.339%   $136.4793   $136.48   $136.50   $136.50  
  Purchase #3 $14.78   4.543%   $15.4515   $15.45   $15.45   $15.50  
  Purchase #4 $182.59   12.177%   $204.824   $204.82   $204.80   $204.80  
  Purchase #5 $190.78   6.777%   $203.7092   $203.71   $203.70   $203.70  
  Purchase #6 $108.47   3.525%   $112.2936   $112.29   $112.30   $112.30  
  Purchase #7 $129.55   11.727%   $144.7423   $144.74   $144.75   $144.70  
  7 purchase totals = $832.34       $911.7033   $911.69   $911.70   $911.70