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 $204.98   3.277%   $211.6972   $211.70   $211.70   $211.70  
  Purchase #2 $234.49   13.724%   $266.6714   $266.67   $266.65   $266.70  
  Purchase #3 $193.27   5.660%   $204.2091   $204.21   $204.20   $204.20  
  Purchase #4 $238.67   4.862%   $250.2741   $250.27   $250.25   $250.30  
  Purchase #5 $159.66   9.749%   $175.2253   $175.23   $175.25   $175.20  
  Purchase #6 $178.76   12.579%   $201.2462   $201.25   $201.25   $201.20  
  Purchase #7 $169.89   8.595%   $184.492   $184.49   $184.50   $184.50  
  7 purchase totals = $1,379.72       $1,493.8153   $1,493.82   $1,493.80   $1,493.80