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 $214.87   6.569%   $228.9848   $228.98   $229.00   $229.00  
  Purchase #2 $76.79   6.175%   $81.5318   $81.53   $81.55   $81.50  
  Purchase #3 $217.27   8.713%   $236.2007   $236.20   $236.20   $236.20  
  Purchase #4 $97.74   3.385%   $101.0485   $101.05   $101.05   $101.00  
  Purchase #5 $6.90   8.271%   $7.4707   $7.47   $7.45   $7.50  
  Purchase #6 $247.44   4.218%   $257.877   $257.88   $257.90   $257.90  
  Purchase #7 $236.80   6.367%   $251.8771   $251.88   $251.90   $251.90  
  7 purchase totals = $1,097.81       $1,164.9906   $1,164.99   $1,165.05   $1,165.00