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 $179.96   3.366%   $186.0175   $186.02   $186.00   $186.00  
  Purchase #2 $245.67   3.743%   $254.8654   $254.87   $254.85   $254.90  
  Purchase #3 $213.72   13.576%   $242.7346   $242.73   $242.75   $242.70  
  Purchase #4 $120.36   3.586%   $124.6761   $124.68   $124.70   $124.70  
  Purchase #5 $198.74   6.781%   $212.2166   $212.22   $212.20   $212.20  
  Purchase #6 $50.40   6.223%   $53.5364   $53.54   $53.55   $53.50  
  Purchase #7 $168.61   4.721%   $176.5701   $176.57   $176.55   $176.60  
  7 purchase totals = $1,177.46       $1,250.6167   $1,250.63   $1,250.60   $1,250.60