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 $92.93   5.751%   $98.2744   $98.27   $98.25   $98.30  
  Purchase #2 $48.82   5.591%   $51.5495   $51.55   $51.55   $51.50  
  Purchase #3 $121.86   13.186%   $137.9285   $137.93   $137.95   $137.90  
  Purchase #4 $232.59   3.420%   $240.5446   $240.54   $240.55   $240.50  
  Purchase #5 $237.37   13.303%   $268.9473   $268.95   $268.95   $268.90  
  Purchase #6 $126.75   3.843%   $131.621   $131.62   $131.60   $131.60  
  Purchase #7 $119.46   8.354%   $129.4397   $129.44   $129.45   $129.40  
  7 purchase totals = $979.78       $1,058.3050   $1,058.30   $1,058.30   $1,058.10