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 $243.78   6.330%   $259.2113   $259.21   $259.20   $259.20  
  Purchase #2 $77.66   5.537%   $81.96   $81.96   $81.95   $82.00  
  Purchase #3 $63.44   11.355%   $70.6436   $70.64   $70.65   $70.60  
  Purchase #4 $47.80   10.639%   $52.8854   $52.89   $52.90   $52.90  
  Purchase #5 $211.55   11.675%   $236.2485   $236.25   $236.25   $236.20  
  Purchase #6 $215.45   5.337%   $226.9486   $226.95   $226.95   $226.90  
  Purchase #7 $199.42   12.704%   $224.7543   $224.75   $224.75   $224.80  
  7 purchase totals = $1,059.10       $1,152.6517   $1,152.65   $1,152.65   $1,152.60