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 $62.70   8.598%   $68.0909   $68.09   $68.10   $68.10  
  Purchase #2 $246.32   5.223%   $259.1853   $259.19   $259.20   $259.20  
  Purchase #3 $150.36   4.851%   $157.654   $157.65   $157.65   $157.70  
  Purchase #4 $144.90   8.732%   $157.5527   $157.55   $157.55   $157.60  
  Purchase #5 $127.32   3.347%   $131.5814   $131.58   $131.60   $131.60  
  Purchase #6 $180.81   4.158%   $188.3281   $188.33   $188.35   $188.30  
  Purchase #7 $241.56   3.109%   $249.0701   $249.07   $249.05   $249.10  
  7 purchase totals = $1,153.97       $1,211.4625   $1,211.46   $1,211.50   $1,211.60