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 $244.88   9.289%   $267.6269   $267.63   $267.65   $267.60  
  Purchase #2 $229.37   13.257%   $259.7776   $259.78   $259.80   $259.80  
  Purchase #3 $170.89   7.336%   $183.4265   $183.43   $183.45   $183.40  
  Purchase #4 $29.81   13.103%   $33.716   $33.72   $33.70   $33.70  
  Purchase #5 $166.51   9.672%   $182.6148   $182.61   $182.60   $182.60  
  Purchase #6 $175.54   10.378%   $193.7575   $193.76   $193.75   $193.80  
  Purchase #7 $13.76   5.151%   $14.4688   $14.47   $14.45   $14.50  
  7 purchase totals = $1,030.76       $1,135.3881   $1,135.40   $1,135.40   $1,135.40