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 $218.97   3.183%   $225.9398   $225.94   $225.95   $225.90  
  Purchase #2 $94.44   6.512%   $100.5899   $100.59   $100.60   $100.60  
  Purchase #3 $31.93   11.737%   $35.6776   $35.68   $35.70   $35.70  
  Purchase #4 $197.64   12.323%   $221.9952   $222.00   $222.00   $222.00  
  Purchase #5 $115.93   6.696%   $123.6927   $123.69   $123.70   $123.70  
  Purchase #6 $191.63   8.151%   $207.2498   $207.25   $207.25   $207.20  
  Purchase #7 $222.61   6.314%   $236.6656   $236.67   $236.65   $236.70  
  7 purchase totals = $1,073.15       $1,151.8106   $1,151.82   $1,151.85   $1,151.80