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 $214.29   12.164%   $240.3562   $240.36   $240.35   $240.40  
  Purchase #2 $208.25   11.623%   $232.4549   $232.45   $232.45   $232.50  
  Purchase #3 $131.31   11.781%   $146.7796   $146.78   $146.80   $146.80  
  Purchase #4 $223.76   11.452%   $249.385   $249.39   $249.40   $249.40  
  Purchase #5 $15.32   12.452%   $17.2276   $17.23   $17.25   $17.20  
  Purchase #6 $128.53   10.441%   $141.9498   $141.95   $141.95   $141.90  
  Purchase #7 $26.57   3.258%   $27.4357   $27.44   $27.45   $27.40  
  7 purchase totals = $948.03       $1,055.5888   $1,055.60   $1,055.65   $1,055.60