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 $180.26   8.343%   $195.2991   $195.30   $195.30   $195.30  
  Purchase #2 $131.85   6.869%   $140.9068   $140.91   $140.90   $140.90  
  Purchase #3 $239.51   7.526%   $257.5355   $257.54   $257.55   $257.50  
  Purchase #4 $47.58   8.517%   $51.6324   $51.63   $51.65   $51.60  
  Purchase #5 $183.78   13.611%   $208.7943   $208.79   $208.80   $208.80  
  Purchase #6 $102.63   10.804%   $113.7181   $113.72   $113.70   $113.70  
  Purchase #7 $224.74   3.809%   $233.3003   $233.30   $233.30   $233.30  
  7 purchase totals = $1,110.35       $1,201.1865   $1,201.19   $1,201.20   $1,201.10