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 $111.56   7.775%   $120.2338   $120.23   $120.25   $120.20  
  Purchase #2 $186.63   3.537%   $193.2311   $193.23   $193.25   $193.20  
  Purchase #3 $214.58   9.450%   $234.8578   $234.86   $234.85   $234.90  
  Purchase #4 $241.35   3.680%   $250.2317   $250.23   $250.25   $250.20  
  Purchase #5 $120.51   8.715%   $131.0124   $131.01   $131.00   $131.00  
  Purchase #6 $23.37   7.275%   $25.0702   $25.07   $25.05   $25.10  
  Purchase #7 $92.57   13.374%   $104.9503   $104.95   $104.95   $105.00  
  7 purchase totals = $990.57       $1,059.5873   $1,059.58   $1,059.60   $1,059.60