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 $141.75   4.208%   $147.7148   $147.71   $147.70   $147.70  
  Purchase #2 $30.93   13.186%   $35.0084   $35.01   $35.00   $35.00  
  Purchase #3 $213.90   12.532%   $240.7059   $240.71   $240.70   $240.70  
  Purchase #4 $167.49   7.162%   $179.4856   $179.49   $179.50   $179.50  
  Purchase #5 $182.48   3.733%   $189.292   $189.29   $189.30   $189.30  
  Purchase #6 $152.63   3.612%   $158.143   $158.14   $158.15   $158.10  
  Purchase #7 $230.35   11.333%   $256.4556   $256.46   $256.45   $256.50  
  7 purchase totals = $1,119.53       $1,206.8053   $1,206.81   $1,206.80   $1,206.80