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 $238.41   7.226%   $255.6375   $255.64   $255.65   $255.60  
  Purchase #2 $70.58   9.111%   $77.0105   $77.01   $77.00   $77.00  
  Purchase #3 $185.44   9.115%   $202.3429   $202.34   $202.35   $202.30  
  Purchase #4 $49.51   9.280%   $54.1045   $54.10   $54.10   $54.10  
  Purchase #5 $81.75   5.627%   $86.3501   $86.35   $86.35   $86.40  
  Purchase #6 $129.62   11.233%   $144.1802   $144.18   $144.20   $144.20  
  Purchase #7 $214.60   5.794%   $227.0339   $227.03   $227.05   $227.00  
  7 purchase totals = $969.91       $1,046.6596   $1,046.65   $1,046.70   $1,046.60