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 $26.95   8.657%   $29.2831   $29.28   $29.30   $29.30  
  Purchase #2 $234.75   6.471%   $249.9407   $249.94   $249.95   $249.90  
  Purchase #3 $65.94   5.475%   $69.5502   $69.55   $69.55   $69.60  
  Purchase #4 $128.59   10.357%   $141.9081   $141.91   $141.90   $141.90  
  Purchase #5 $238.99   9.685%   $262.1362   $262.14   $262.15   $262.10  
  Purchase #6 $35.62   6.381%   $37.8929   $37.89   $37.90   $37.90  
  Purchase #7 $15.32   9.456%   $16.7687   $16.77   $16.75   $16.80  
  7 purchase totals = $746.16       $807.4799   $807.48   $807.50   $807.50