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 $222.54   10.673%   $246.2917   $246.29   $246.30   $246.30  
  Purchase #2 $246.32   8.599%   $267.5011   $267.50   $267.50   $267.50  
  Purchase #3 $138.70   9.420%   $151.7655   $151.77   $151.75   $151.80  
  Purchase #4 $109.46   4.841%   $114.759   $114.76   $114.75   $114.80  
  Purchase #5 $197.34   11.268%   $219.5763   $219.58   $219.60   $219.60  
  Purchase #6 $182.51   6.520%   $194.4097   $194.41   $194.40   $194.40  
  Purchase #7 $132.65   11.865%   $148.3889   $148.39   $148.40   $148.40  
  7 purchase totals = $1,229.52       $1,342.6922   $1,342.70   $1,342.70   $1,342.80