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 $208.70   13.326%   $236.5114   $236.51   $236.50   $236.50  
  Purchase #2 $55.57   8.872%   $60.5002   $60.50   $60.50   $60.50  
  Purchase #3 $224.28   6.323%   $238.4612   $238.46   $238.45   $238.50  
  Purchase #4 $104.64   7.551%   $112.5414   $112.54   $112.55   $112.50  
  Purchase #5 $147.90   10.825%   $163.9102   $163.91   $163.90   $163.90  
  Purchase #6 $74.79   7.370%   $80.302   $80.30   $80.30   $80.30  
  Purchase #7 $195.50   11.113%   $217.2259   $217.23   $217.25   $217.20  
  7 purchase totals = $1,011.38       $1,109.4523   $1,109.45   $1,109.45   $1,109.40