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 $118.47   6.601%   $126.2902   $126.29   $126.30   $126.30  
  Purchase #2 $107.75   9.490%   $117.9755   $117.98   $118.00   $118.00  
  Purchase #3 $15.50   5.286%   $16.3193   $16.32   $16.30   $16.30  
  Purchase #4 $163.74   11.483%   $182.5423   $182.54   $182.55   $182.50  
  Purchase #5 $163.30   8.387%   $176.996   $177.00   $177.00   $177.00  
  Purchase #6 $51.65   3.682%   $53.5518   $53.55   $53.55   $53.60  
  Purchase #7 $142.38   7.239%   $152.6869   $152.69   $152.70   $152.70  
  7 purchase totals = $762.79       $826.3620   $826.37   $826.40   $826.40