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 $111.51   13.357%   $126.4044   $126.40   $126.40   $126.40  
  Purchase #2 $52.80   12.866%   $59.5932   $59.59   $59.60   $59.60  
  Purchase #3 $158.54   11.676%   $177.0511   $177.05   $177.05   $177.10  
  Purchase #4 $63.90   4.267%   $66.6266   $66.63   $66.65   $66.60  
  Purchase #5 $208.92   9.291%   $228.3308   $228.33   $228.35   $228.30  
  Purchase #6 $107.39   10.476%   $118.6402   $118.64   $118.65   $118.60  
  Purchase #7 $44.85   10.330%   $49.483   $49.48   $49.50   $49.50  
  7 purchase totals = $747.91       $826.1293   $826.12   $826.20   $826.10