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 $136.38   8.735%   $148.2928   $148.29   $148.30   $148.30  
  Purchase #2 $218.62   7.662%   $235.3707   $235.37   $235.35   $235.40  
  Purchase #3 $188.29   9.424%   $206.0344   $206.03   $206.05   $206.00  
  Purchase #4 $130.91   3.872%   $135.9788   $135.98   $136.00   $136.00  
  Purchase #5 $180.25   9.531%   $197.4296   $197.43   $197.45   $197.40  
  Purchase #6 $82.81   11.857%   $92.6288   $92.63   $92.65   $92.60  
  Purchase #7 $174.41   4.505%   $182.2672   $182.27   $182.25   $182.30  
  7 purchase totals = $1,111.67       $1,198.0023   $1,198.00   $1,198.05   $1,198.00