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 $221.46   8.803%   $240.9551   $240.96   $240.95   $241.00  
  Purchase #2 $148.39   3.522%   $153.6163   $153.62   $153.60   $153.60  
  Purchase #3 $173.90   10.640%   $192.403   $192.40   $192.40   $192.40  
  Purchase #4 $206.62   7.872%   $222.8851   $222.89   $222.90   $222.90  
  Purchase #5 $51.96   11.671%   $58.0243   $58.02   $58.00   $58.00  
  Purchase #6 $167.47   12.766%   $188.8492   $188.85   $188.85   $188.80  
  Purchase #7 $16.37   12.462%   $18.41   $18.41   $18.40   $18.40  
  7 purchase totals = $986.17       $1,075.1430   $1,075.15   $1,075.10   $1,075.10