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 $212.97   6.235%   $226.2487   $226.25   $226.25   $226.20  
  Purchase #2 $176.84   4.753%   $185.2452   $185.25   $185.25   $185.20  
  Purchase #3 $226.71   4.407%   $236.7011   $236.70   $236.70   $236.70  
  Purchase #4 $122.67   4.306%   $127.9522   $127.95   $127.95   $128.00  
  Purchase #5 $206.97   8.494%   $224.55   $224.55   $224.55   $224.60  
  Purchase #6 $171.81   8.834%   $186.9877   $186.99   $187.00   $187.00  
  Purchase #7 $133.77   8.252%   $144.8087   $144.81   $144.80   $144.80  
  7 purchase totals = $1,251.74       $1,332.4936   $1,332.50   $1,332.50   $1,332.50