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 $207.88   11.331%   $231.4349   $231.43   $231.45   $231.40  
  Purchase #2 $16.33   9.357%   $17.858   $17.86   $17.85   $17.90  
  Purchase #3 $38.94   7.140%   $41.7203   $41.72   $41.70   $41.70  
  Purchase #4 $188.57   3.746%   $195.6338   $195.63   $195.65   $195.60  
  Purchase #5 $178.69   10.607%   $197.6436   $197.64   $197.65   $197.60  
  Purchase #6 $36.30   11.644%   $40.5268   $40.53   $40.55   $40.50  
  Purchase #7 $51.88   8.715%   $56.4013   $56.40   $56.40   $56.40  
  7 purchase totals = $718.59       $781.2187   $781.21   $781.25   $781.10