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 $246.89   5.512%   $260.4986   $260.50   $260.50   $260.50  
  Purchase #2 $183.48   7.753%   $197.7052   $197.71   $197.70   $197.70  
  Purchase #3 $166.90   12.856%   $188.3567   $188.36   $188.35   $188.40  
  Purchase #4 $24.59   3.563%   $25.4661   $25.47   $25.45   $25.50  
  Purchase #5 $86.64   6.697%   $92.4423   $92.44   $92.45   $92.40  
  Purchase #6 $201.25   13.238%   $227.8915   $227.89   $227.90   $227.90  
  Purchase #7 $53.43   12.391%   $60.0505   $60.05   $60.05   $60.10  
  7 purchase totals = $963.18       $1,052.4109   $1,052.42   $1,052.40   $1,052.50