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 $196.75   13.843%   $223.9861   $223.99   $224.00   $224.00  
  Purchase #2 $128.55   9.629%   $140.9281   $140.93   $140.95   $140.90  
  Purchase #3 $105.63   8.495%   $114.6033   $114.60   $114.60   $114.60  
  Purchase #4 $30.41   6.656%   $32.4341   $32.43   $32.45   $32.40  
  Purchase #5 $211.54   11.756%   $236.4086   $236.41   $236.40   $236.40  
  Purchase #6 $137.39   9.774%   $150.8185   $150.82   $150.80   $150.80  
  Purchase #7 $114.86   11.601%   $128.1849   $128.18   $128.20   $128.20  
  7 purchase totals = $925.13       $1,027.3636   $1,027.36   $1,027.40   $1,027.30