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 $90.47   5.110%   $95.093   $95.09   $95.10   $95.10  
  Purchase #2 $150.77   9.472%   $165.0509   $165.05   $165.05   $165.10  
  Purchase #3 $208.66   12.167%   $234.0477   $234.05   $234.05   $234.00  
  Purchase #4 $84.97   13.233%   $96.2141   $96.21   $96.20   $96.20  
  Purchase #5 $206.63   11.404%   $230.1941   $230.19   $230.20   $230.20  
  Purchase #6 $244.74   8.565%   $265.702   $265.70   $265.70   $265.70  
  Purchase #7 $234.69   7.652%   $252.6485   $252.65   $252.65   $252.60  
  7 purchase totals = $1,220.93       $1,338.9503   $1,338.94   $1,338.95   $1,338.90