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 $79.54   8.726%   $86.4807   $86.48   $86.50   $86.50  
  Purchase #2 $177.63   3.407%   $183.6819   $183.68   $183.70   $183.70  
  Purchase #3 $118.56   9.261%   $129.5398   $129.54   $129.55   $129.50  
  Purchase #4 $200.79   8.336%   $217.5279   $217.53   $217.55   $217.50  
  Purchase #5 $109.29   9.692%   $119.8824   $119.88   $119.90   $119.90  
  Purchase #6 $74.62   11.162%   $82.9491   $82.95   $82.95   $82.90  
  Purchase #7 $245.48   8.799%   $267.0798   $267.08   $267.10   $267.10  
  7 purchase totals = $1,005.91       $1,087.1416   $1,087.14   $1,087.25   $1,087.10