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 $156.64   11.602%   $174.8134   $174.81   $174.80   $174.80  
  Purchase #2 $69.45   13.206%   $78.6216   $78.62   $78.60   $78.60  
  Purchase #3 $144.56   3.464%   $149.5676   $149.57   $149.55   $149.60  
  Purchase #4 $193.68   8.391%   $209.9317   $209.93   $209.95   $209.90  
  Purchase #5 $148.90   4.734%   $155.9489   $155.95   $155.95   $155.90  
  Purchase #6 $248.82   3.505%   $257.5411   $257.54   $257.55   $257.50  
  Purchase #7 $36.95   11.492%   $41.1963   $41.20   $41.20   $41.20  
  7 purchase totals = $999.00       $1,067.6206   $1,067.62   $1,067.60   $1,067.50