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 $233.38   13.313%   $264.4499   $264.45   $264.45   $264.40  
  Purchase #2 $194.92   7.340%   $209.2271   $209.23   $209.25   $209.20  
  Purchase #3 $88.69   10.571%   $98.0654   $98.07   $98.05   $98.10  
  Purchase #4 $176.84   10.481%   $195.3746   $195.37   $195.35   $195.40  
  Purchase #5 $38.25   13.528%   $43.4245   $43.42   $43.40   $43.40  
  Purchase #6 $73.47   5.572%   $77.5637   $77.56   $77.55   $77.60  
  Purchase #7 $163.69   9.338%   $178.9754   $178.98   $179.00   $179.00  
  7 purchase totals = $969.24       $1,067.0806   $1,067.08   $1,067.05   $1,067.10