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 $184.68   9.715%   $202.6217   $202.62   $202.60   $202.60  
  Purchase #2 $249.81   11.624%   $278.8479   $278.85   $278.85   $278.80  
  Purchase #3 $53.66   9.448%   $58.7298   $58.73   $58.75   $58.70  
  Purchase #4 $124.63   10.519%   $137.7398   $137.74   $137.75   $137.70  
  Purchase #5 $201.28   5.524%   $212.3987   $212.40   $212.40   $212.40  
  Purchase #6 $69.34   11.513%   $77.3231   $77.32   $77.30   $77.30  
  Purchase #7 $22.32   9.465%   $24.4326   $24.43   $24.45   $24.40  
  7 purchase totals = $905.72       $992.0936   $992.09   $992.10   $991.90