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 $147.60   4.717%   $154.5623   $154.56   $154.55   $154.60  
  Purchase #2 $119.70   5.226%   $125.9555   $125.96   $125.95   $126.00  
  Purchase #3 $113.30   12.588%   $127.5622   $127.56   $127.55   $127.60  
  Purchase #4 $237.89   4.290%   $248.0955   $248.10   $248.10   $248.10  
  Purchase #5 $42.76   7.706%   $46.0551   $46.06   $46.05   $46.10  
  Purchase #6 $138.97   3.603%   $143.9771   $143.98   $144.00   $144.00  
  Purchase #7 $93.57   12.315%   $105.0931   $105.09   $105.10   $105.10  
  7 purchase totals = $893.79       $951.3008   $951.31   $951.30   $951.50