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 $246.98   11.850%   $276.2471   $276.25   $276.25   $276.20  
  Purchase #2 $175.32   11.195%   $194.9471   $194.95   $194.95   $194.90  
  Purchase #3 $250.76   3.432%   $259.3661   $259.37   $259.35   $259.40  
  Purchase #4 $54.99   10.557%   $60.7953   $60.80   $60.80   $60.80  
  Purchase #5 $212.84   11.225%   $236.7313   $236.73   $236.75   $236.70  
  Purchase #6 $161.71   7.768%   $174.2716   $174.27   $174.25   $174.30  
  Purchase #7 $117.72   11.298%   $131.02   $131.02   $131.00   $131.00  
  7 purchase totals = $1,220.32       $1,333.3785   $1,333.39   $1,333.35   $1,333.30