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 $177.30   3.257%   $183.0747   $183.07   $183.05   $183.10  
  Purchase #2 $197.46   5.653%   $208.6224   $208.62   $208.60   $208.60  
  Purchase #3 $34.75   8.414%   $37.6739   $37.67   $37.65   $37.70  
  Purchase #4 $249.93   13.376%   $283.3606   $283.36   $283.35   $283.40  
  Purchase #5 $38.83   13.622%   $44.1194   $44.12   $44.10   $44.10  
  Purchase #6 $185.86   5.193%   $195.5117   $195.51   $195.50   $195.50  
  Purchase #7 $67.83   8.178%   $73.3771   $73.38   $73.40   $73.40  
  7 purchase totals = $951.96       $1,025.7398   $1,025.73   $1,025.65   $1,025.80