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 $182.63   11.504%   $203.6398   $203.64   $203.65   $203.60  
  Purchase #2 $114.68   4.517%   $119.8601   $119.86   $119.85   $119.90  
  Purchase #3 $218.85   5.659%   $231.2347   $231.23   $231.25   $231.20  
  Purchase #4 $63.28   4.745%   $66.2826   $66.28   $66.30   $66.30  
  Purchase #5 $187.85   13.786%   $213.747   $213.75   $213.75   $213.70  
  Purchase #6 $97.45   11.618%   $108.7717   $108.77   $108.75   $108.80  
  Purchase #7 $29.46   13.718%   $33.5013   $33.50   $33.50   $33.50  
  7 purchase totals = $894.20       $977.0372   $977.03   $977.05   $977.00