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 $94.47   11.810%   $105.6269   $105.63   $105.65   $105.60  
  Purchase #2 $182.79   9.736%   $200.5864   $200.59   $200.60   $200.60  
  Purchase #3 $177.53   5.647%   $187.5551   $187.56   $187.55   $187.60  
  Purchase #4 $28.50   6.811%   $30.4411   $30.44   $30.45   $30.40  
  Purchase #5 $223.67   12.847%   $252.4049   $252.40   $252.40   $252.40  
  Purchase #6 $222.89   5.299%   $234.7009   $234.70   $234.70   $234.70  
  Purchase #7 $10.26   13.314%   $11.626   $11.63   $11.65   $11.60  
  7 purchase totals = $940.11       $1,022.9413   $1,022.95   $1,023.00   $1,022.90