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 $54.99   11.303%   $61.2055   $61.21   $61.20   $61.20  
  Purchase #2 $196.60   10.665%   $217.5674   $217.57   $217.55   $217.60  
  Purchase #3 $102.58   12.849%   $115.7605   $115.76   $115.75   $115.80  
  Purchase #4 $60.83   3.457%   $62.9329   $62.93   $62.95   $62.90  
  Purchase #5 $104.87   7.231%   $112.4531   $112.45   $112.45   $112.50  
  Purchase #6 $67.62   7.276%   $72.54   $72.54   $72.55   $72.50  
  Purchase #7 $153.25   6.782%   $163.6434   $163.64   $163.65   $163.60  
  7 purchase totals = $740.74       $806.1028   $806.10   $806.10   $806.10