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 $30.80   7.584%   $33.1359   $33.14   $33.15   $33.10  
  Purchase #2 $125.93   10.622%   $139.3063   $139.31   $139.30   $139.30  
  Purchase #3 $207.71   5.252%   $218.6189   $218.62   $218.60   $218.60  
  Purchase #4 $231.58   3.411%   $239.4792   $239.48   $239.50   $239.50  
  Purchase #5 $15.88   7.510%   $17.0726   $17.07   $17.05   $17.10  
  Purchase #6 $56.60   11.304%   $62.9981   $63.00   $63.00   $63.00  
  Purchase #7 $209.76   10.207%   $231.1702   $231.17   $231.15   $231.20  
  7 purchase totals = $878.26       $941.7812   $941.79   $941.75   $941.80