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 $192.68   8.426%   $208.9152   $208.92   $208.90   $208.90  
  Purchase #2 $227.73   5.556%   $240.3827   $240.38   $240.40   $240.40  
  Purchase #3 $34.58   4.712%   $36.2094   $36.21   $36.20   $36.20  
  Purchase #4 $238.32   8.507%   $258.5939   $258.59   $258.60   $258.60  
  Purchase #5 $82.27   7.601%   $88.5233   $88.52   $88.50   $88.50  
  Purchase #6 $54.56   7.204%   $58.4905   $58.49   $58.50   $58.50  
  Purchase #7 $49.93   8.690%   $54.2689   $54.27   $54.25   $54.30  
  7 purchase totals = $880.07       $945.3839   $945.38   $945.35   $945.40