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 $234.59   6.718%   $250.3498   $250.35   $250.35   $250.30  
  Purchase #2 $134.32   4.835%   $140.8144   $140.81   $140.80   $140.80  
  Purchase #3 $155.83   5.845%   $164.9383   $164.94   $164.95   $164.90  
  Purchase #4 $91.63   4.284%   $95.5554   $95.56   $95.55   $95.60  
  Purchase #5 $218.41   12.562%   $245.8467   $245.85   $245.85   $245.80  
  Purchase #6 $201.82   5.554%   $213.0291   $213.03   $213.05   $213.00  
  Purchase #7 $85.80   12.693%   $96.6906   $96.69   $96.70   $96.70  
  7 purchase totals = $1,122.40       $1,207.2243   $1,207.23   $1,207.25   $1,207.10