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 $181.95   9.689%   $199.5791   $199.58   $199.60   $199.60  
  Purchase #2 $181.53   13.301%   $205.6753   $205.68   $205.70   $205.70  
  Purchase #3 $11.62   8.873%   $12.651   $12.65   $12.65   $12.70  
  Purchase #4 $229.36   4.522%   $239.7317   $239.73   $239.75   $239.70  
  Purchase #5 $182.35   13.834%   $207.5763   $207.58   $207.60   $207.60  
  Purchase #6 $52.35   8.104%   $56.5924   $56.59   $56.60   $56.60  
  Purchase #7 $86.88   12.597%   $97.8243   $97.82   $97.80   $97.80  
  7 purchase totals = $926.04       $1,019.6301   $1,019.63   $1,019.70   $1,019.70