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 $246.28   6.220%   $261.5986   $261.60   $261.60   $261.60  
  Purchase #2 $5.95   3.197%   $6.1402   $6.14   $6.15   $6.10  
  Purchase #3 $242.46   12.449%   $272.6438   $272.64   $272.65   $272.60  
  Purchase #4 $12.89   3.793%   $13.3789   $13.38   $13.40   $13.40  
  Purchase #5 $107.29   8.776%   $116.7058   $116.71   $116.70   $116.70  
  Purchase #6 $210.25   3.274%   $217.1336   $217.13   $217.15   $217.10  
  Purchase #7 $33.86   12.202%   $37.9916   $37.99   $38.00   $38.00  
  7 purchase totals = $858.98       $925.5925   $925.59   $925.65   $925.50