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 $58.46   8.792%   $63.5998   $63.60   $63.60   $63.60  
  Purchase #2 $219.59   11.150%   $244.0743   $244.07   $244.05   $244.10  
  Purchase #3 $63.99   13.320%   $72.5135   $72.51   $72.50   $72.50  
  Purchase #4 $226.34   11.401%   $252.145   $252.15   $252.15   $252.10  
  Purchase #5 $9.51   10.488%   $10.5074   $10.51   $10.50   $10.50  
  Purchase #6 $171.82   6.227%   $182.5192   $182.52   $182.50   $182.50  
  Purchase #7 $90.66   8.324%   $98.2065   $98.21   $98.20   $98.20  
  7 purchase totals = $840.37       $923.5657   $923.57   $923.50   $923.50