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 $57.62   10.613%   $63.7352   $63.74   $63.75   $63.70  
  Purchase #2 $177.82   3.239%   $183.5796   $183.58   $183.60   $183.60  
  Purchase #3 $199.38   13.422%   $226.1408   $226.14   $226.15   $226.10  
  Purchase #4 $151.40   6.378%   $161.0563   $161.06   $161.05   $161.10  
  Purchase #5 $43.75   6.508%   $46.5973   $46.60   $46.60   $46.60  
  Purchase #6 $95.82   8.786%   $104.2387   $104.24   $104.25   $104.20  
  Purchase #7 $212.40   13.704%   $241.5073   $241.51   $241.50   $241.50  
  7 purchase totals = $938.19       $1,026.8552   $1,026.87   $1,026.90   $1,026.80