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 $216.78   9.262%   $236.8582   $236.86   $236.85   $236.90  
  Purchase #2 $144.81   5.352%   $152.5602   $152.56   $152.55   $152.60  
  Purchase #3 $17.66   7.482%   $18.9813   $18.98   $19.00   $19.00  
  Purchase #4 $143.78   3.266%   $148.4759   $148.48   $148.50   $148.50  
  Purchase #5 $126.50   11.670%   $141.2626   $141.26   $141.25   $141.30  
  Purchase #6 $52.57   6.566%   $56.0217   $56.02   $56.00   $56.00  
  Purchase #7 $20.28   3.672%   $21.0247   $21.02   $21.00   $21.00  
  7 purchase totals = $722.38       $775.1846   $775.18   $775.15   $775.30