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 $250.58   4.585%   $262.0691   $262.07   $262.05   $262.10  
  Purchase #2 $226.38   12.611%   $254.9288   $254.93   $254.95   $254.90  
  Purchase #3 $203.54   12.184%   $228.3393   $228.34   $228.35   $228.30  
  Purchase #4 $46.84   12.664%   $52.7718   $52.77   $52.75   $52.80  
  Purchase #5 $47.71   5.428%   $50.2997   $50.30   $50.30   $50.30  
  Purchase #6 $77.33   13.153%   $87.5012   $87.50   $87.50   $87.50  
  Purchase #7 $126.63   12.264%   $142.1599   $142.16   $142.15   $142.20  
  7 purchase totals = $979.01       $1,078.0698   $1,078.07   $1,078.05   $1,078.10