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 $224.55   13.218%   $254.231   $254.23   $254.25   $254.20  
  Purchase #2 $175.28   6.429%   $186.5488   $186.55   $186.55   $186.50  
  Purchase #3 $60.99   7.563%   $65.6027   $65.60   $65.60   $65.60  
  Purchase #4 $184.85   12.706%   $208.337   $208.34   $208.35   $208.30  
  Purchase #5 $220.99   13.586%   $251.0137   $251.01   $251.00   $251.00  
  Purchase #6 $35.81   3.379%   $37.02   $37.02   $37.00   $37.00  
  Purchase #7 $218.42   11.233%   $242.9551   $242.96   $242.95   $243.00  
  7 purchase totals = $1,120.89       $1,245.7083   $1,245.71   $1,245.70   $1,245.60