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 $219.88   13.720%   $250.0475   $250.05   $250.05   $250.00  
  Purchase #2 $187.59   9.648%   $205.6887   $205.69   $205.70   $205.70  
  Purchase #3 $41.69   11.625%   $46.5365   $46.54   $46.55   $46.50  
  Purchase #4 $234.82   5.337%   $247.3523   $247.35   $247.35   $247.40  
  Purchase #5 $206.94   10.857%   $229.4075   $229.41   $229.40   $229.40  
  Purchase #6 $100.59   8.697%   $109.3383   $109.34   $109.35   $109.30  
  Purchase #7 $120.92   8.665%   $131.3977   $131.40   $131.40   $131.40  
  7 purchase totals = $1,112.43       $1,219.7685   $1,219.78   $1,219.80   $1,219.70