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 $197.95   8.416%   $214.6095   $214.61   $214.60   $214.60  
  Purchase #2 $23.34   13.721%   $26.5425   $26.54   $26.55   $26.50  
  Purchase #3 $163.38   8.447%   $177.1807   $177.18   $177.20   $177.20  
  Purchase #4 $157.95   11.602%   $176.2754   $176.28   $176.30   $176.30  
  Purchase #5 $35.64   8.780%   $38.7692   $38.77   $38.75   $38.80  
  Purchase #6 $200.57   10.660%   $221.9508   $221.95   $221.95   $222.00  
  Purchase #7 $139.48   5.424%   $147.0454   $147.05   $147.05   $147.00  
  7 purchase totals = $918.31       $1,002.3735   $1,002.38   $1,002.40   $1,002.40