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 $78.65   8.124%   $85.0395   $85.04   $85.05   $85.00  
  Purchase #2 $113.55   8.468%   $123.1654   $123.17   $123.15   $123.20  
  Purchase #3 $202.55   6.569%   $215.8555   $215.86   $215.85   $215.90  
  Purchase #4 $179.43   10.195%   $197.7229   $197.72   $197.70   $197.70  
  Purchase #5 $145.96   8.311%   $158.0907   $158.09   $158.10   $158.10  
  Purchase #6 $239.48   12.377%   $269.1204   $269.12   $269.10   $269.10  
  Purchase #7 $233.90   6.471%   $249.0357   $249.04   $249.05   $249.00  
  7 purchase totals = $1,193.52       $1,298.0301   $1,298.04   $1,298.00   $1,298.00