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 $13.66   8.296%   $14.7932   $14.79   $14.80   $14.80  
  Purchase #2 $139.63   11.320%   $155.4361   $155.44   $155.45   $155.40  
  Purchase #3 $165.58   12.356%   $186.0391   $186.04   $186.05   $186.00  
  Purchase #4 $214.54   10.758%   $237.6202   $237.62   $237.60   $237.60  
  Purchase #5 $224.29   10.599%   $248.0625   $248.06   $248.05   $248.10  
  Purchase #6 $138.34   9.633%   $151.6663   $151.67   $151.65   $151.70  
  Purchase #7 $250.25   9.614%   $274.309   $274.31   $274.30   $274.30  
  7 purchase totals = $1,146.29       $1,267.9264   $1,267.93   $1,267.90   $1,267.90