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 $188.81   13.441%   $214.188   $214.19   $214.20   $214.20  
  Purchase #2 $242.42   4.298%   $252.8392   $252.84   $252.85   $252.80  
  Purchase #3 $70.73   5.468%   $74.5975   $74.60   $74.60   $74.60  
  Purchase #4 $52.60   12.422%   $59.134   $59.13   $59.15   $59.10  
  Purchase #5 $227.60   4.329%   $237.4528   $237.45   $237.45   $237.50  
  Purchase #6 $239.94   4.221%   $250.0679   $250.07   $250.05   $250.10  
  Purchase #7 $246.91   9.847%   $271.2232   $271.22   $271.20   $271.20  
  7 purchase totals = $1,269.01       $1,359.5026   $1,359.50   $1,359.50   $1,359.50