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 $126.47   7.691%   $136.1968   $136.20   $136.20   $136.20  
  Purchase #2 $97.53   6.388%   $103.7602   $103.76   $103.75   $103.80  
  Purchase #3 $207.94   3.193%   $214.5795   $214.58   $214.60   $214.60  
  Purchase #4 $59.45   4.798%   $62.3024   $62.30   $62.30   $62.30  
  Purchase #5 $127.44   8.587%   $138.3833   $138.38   $138.40   $138.40  
  Purchase #6 $147.91   6.491%   $157.5108   $157.51   $157.50   $157.50  
  Purchase #7 $235.43   6.400%   $250.4975   $250.50   $250.50   $250.50  
  7 purchase totals = $1,002.17       $1,063.2305   $1,063.23   $1,063.25   $1,063.30