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 $224.93   10.714%   $249.029   $249.03   $249.05   $249.00  
  Purchase #2 $171.65   12.235%   $192.6514   $192.65   $192.65   $192.70  
  Purchase #3 $88.77   7.758%   $95.6568   $95.66   $95.65   $95.70  
  Purchase #4 $250.37   10.640%   $277.0094   $277.01   $277.00   $277.00  
  Purchase #5 $41.63   3.406%   $43.0479   $43.05   $43.05   $43.00  
  Purchase #6 $39.48   10.342%   $43.563   $43.56   $43.55   $43.60  
  Purchase #7 $58.68   7.867%   $63.2964   $63.30   $63.30   $63.30  
  7 purchase totals = $875.51       $964.2539   $964.26   $964.25   $964.30