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 $227.45   8.247%   $246.2078   $246.21   $246.20   $246.20  
  Purchase #2 $11.34   9.266%   $12.3908   $12.39   $12.40   $12.40  
  Purchase #3 $177.28   7.626%   $190.7994   $190.80   $190.80   $190.80  
  Purchase #4 $226.26   10.474%   $249.9585   $249.96   $249.95   $250.00  
  Purchase #5 $238.91   11.236%   $265.7539   $265.75   $265.75   $265.80  
  Purchase #6 $229.34   7.238%   $245.9396   $245.94   $245.95   $245.90  
  Purchase #7 $245.32   10.163%   $270.2519   $270.25   $270.25   $270.30  
  7 purchase totals = $1,355.90       $1,481.3019   $1,481.30   $1,481.30   $1,481.40