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 $55.42   5.792%   $58.6299   $58.63   $58.65   $58.60  
  Purchase #2 $229.59   3.519%   $237.6693   $237.67   $237.65   $237.70  
  Purchase #3 $181.96   8.139%   $196.7697   $196.77   $196.75   $196.80  
  Purchase #4 $121.55   12.521%   $136.7693   $136.77   $136.75   $136.80  
  Purchase #5 $152.58   12.223%   $171.2299   $171.23   $171.25   $171.20  
  Purchase #6 $186.88   10.821%   $207.1023   $207.10   $207.10   $207.10  
  Purchase #7 $118.96   5.445%   $125.4374   $125.44   $125.45   $125.40  
  7 purchase totals = $1,046.94       $1,133.6078   $1,133.61   $1,133.60   $1,133.60