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 $183.76   10.815%   $203.6336   $203.63   $203.65   $203.60  
  Purchase #2 $88.46   7.293%   $94.9114   $94.91   $94.90   $94.90  
  Purchase #3 $198.37   9.723%   $217.6575   $217.66   $217.65   $217.70  
  Purchase #4 $191.48   6.662%   $204.2364   $204.24   $204.25   $204.20  
  Purchase #5 $206.66   9.681%   $226.6668   $226.67   $226.65   $226.70  
  Purchase #6 $136.85   12.523%   $153.9877   $153.99   $154.00   $154.00  
  Purchase #7 $82.94   10.724%   $91.8345   $91.83   $91.85   $91.80  
  7 purchase totals = $1,088.52       $1,192.9279   $1,192.93   $1,192.95   $1,192.90