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 $177.47   12.696%   $200.0016   $200.00   $200.00   $200.00  
  Purchase #2 $183.83   7.764%   $198.1026   $198.10   $198.10   $198.10  
  Purchase #3 $31.73   3.756%   $32.9218   $32.92   $32.90   $32.90  
  Purchase #4 $114.86   9.334%   $125.581   $125.58   $125.60   $125.60  
  Purchase #5 $83.29   3.119%   $85.8878   $85.89   $85.90   $85.90  
  Purchase #6 $116.79   11.819%   $130.5934   $130.59   $130.60   $130.60  
  Purchase #7 $215.47   9.404%   $235.7328   $235.73   $235.75   $235.70  
  7 purchase totals = $923.44       $1,008.8210   $1,008.81   $1,008.85   $1,008.80