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 $215.34   12.115%   $241.4284   $241.43   $241.45   $241.40  
  Purchase #2 $179.73   13.683%   $204.3225   $204.32   $204.30   $204.30  
  Purchase #3 $66.79   9.708%   $73.274   $73.27   $73.25   $73.30  
  Purchase #4 $213.36   3.837%   $221.5466   $221.55   $221.55   $221.50  
  Purchase #5 $127.92   4.357%   $133.4935   $133.49   $133.50   $133.50  
  Purchase #6 $24.90   13.861%   $28.3514   $28.35   $28.35   $28.40  
  Purchase #7 $226.48   10.168%   $249.5085   $249.51   $249.50   $249.50  
  7 purchase totals = $1,054.52       $1,151.9249   $1,151.92   $1,151.90   $1,151.90