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 $70.36   4.851%   $73.7732   $73.77   $73.75   $73.80  
  Purchase #2 $129.83   10.540%   $143.5141   $143.51   $143.50   $143.50  
  Purchase #3 $162.72   8.206%   $176.0728   $176.07   $176.05   $176.10  
  Purchase #4 $132.28   12.553%   $148.8851   $148.89   $148.90   $148.90  
  Purchase #5 $44.60   13.574%   $50.654   $50.65   $50.65   $50.70  
  Purchase #6 $229.57   12.807%   $258.971   $258.97   $258.95   $259.00  
  Purchase #7 $15.33   11.501%   $17.0931   $17.09   $17.10   $17.10  
  7 purchase totals = $784.69       $868.9633   $868.95   $868.90   $869.10