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 $250.75   10.477%   $277.0211   $277.02   $277.00   $277.00  
  Purchase #2 $186.62   5.188%   $196.3018   $196.30   $196.30   $196.30  
  Purchase #3 $202.31   11.826%   $226.2352   $226.24   $226.25   $226.20  
  Purchase #4 $129.67   6.761%   $138.437   $138.44   $138.45   $138.40  
  Purchase #5 $9.83   5.558%   $10.3764   $10.38   $10.40   $10.40  
  Purchase #6 $140.46   5.509%   $148.1979   $148.20   $148.20   $148.20  
  Purchase #7 $25.37   11.745%   $28.3497   $28.35   $28.35   $28.30  
  7 purchase totals = $945.01       $1,024.9191   $1,024.93   $1,024.95   $1,024.80