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 $104.61   9.704%   $114.7614   $114.76   $114.75   $114.80  
  Purchase #2 $243.61   6.589%   $259.6615   $259.66   $259.65   $259.70  
  Purchase #3 $226.35   10.459%   $250.0239   $250.02   $250.00   $250.00  
  Purchase #4 $23.37   7.201%   $25.0529   $25.05   $25.05   $25.10  
  Purchase #5 $120.63   7.296%   $129.4312   $129.43   $129.45   $129.40  
  Purchase #6 $124.55   11.807%   $139.2556   $139.26   $139.25   $139.30  
  Purchase #7 $28.30   7.317%   $30.3707   $30.37   $30.35   $30.40  
  7 purchase totals = $871.42       $948.5572   $948.55   $948.50   $948.70