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 $42.64   9.391%   $46.6443   $46.64   $46.65   $46.60  
  Purchase #2 $118.33   10.183%   $130.3795   $130.38   $130.40   $130.40  
  Purchase #3 $223.92   7.204%   $240.0512   $240.05   $240.05   $240.10  
  Purchase #4 $173.68   3.397%   $179.5799   $179.58   $179.60   $179.60  
  Purchase #5 $106.46   4.489%   $111.239   $111.24   $111.25   $111.20  
  Purchase #6 $97.91   6.448%   $104.2232   $104.22   $104.20   $104.20  
  Purchase #7 $13.40   6.747%   $14.3041   $14.30   $14.30   $14.30  
  7 purchase totals = $776.34       $826.4212   $826.41   $826.45   $826.40