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 $187.51   11.398%   $208.8824   $208.88   $208.90   $208.90  
  Purchase #2 $192.30   7.281%   $206.3014   $206.30   $206.30   $206.30  
  Purchase #3 $96.45   6.151%   $102.3826   $102.38   $102.40   $102.40  
  Purchase #4 $32.61   12.262%   $36.6086   $36.61   $36.60   $36.60  
  Purchase #5 $217.39   4.712%   $227.6334   $227.63   $227.65   $227.60  
  Purchase #6 $232.64   11.340%   $259.0214   $259.02   $259.00   $259.00  
  Purchase #7 $119.34   5.846%   $126.3166   $126.32   $126.30   $126.30  
  7 purchase totals = $1,078.24       $1,167.1464   $1,167.14   $1,167.15   $1,167.10