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 $125.76   12.496%   $141.475   $141.48   $141.50   $141.50  
  Purchase #2 $33.79   6.196%   $35.8836   $35.88   $35.90   $35.90  
  Purchase #3 $44.74   5.169%   $47.0526   $47.05   $47.05   $47.10  
  Purchase #4 $130.46   3.230%   $134.6739   $134.67   $134.65   $134.70  
  Purchase #5 $209.89   10.723%   $232.3965   $232.40   $232.40   $232.40  
  Purchase #6 $207.88   10.451%   $229.6055   $229.61   $229.60   $229.60  
  Purchase #7 $41.42   3.374%   $42.8175   $42.82   $42.80   $42.80  
  7 purchase totals = $793.94       $863.9046   $863.91   $863.90   $864.00