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 $32.38   11.617%   $36.1416   $36.14   $36.15   $36.10  
  Purchase #2 $241.76   10.683%   $267.5872   $267.59   $267.60   $267.60  
  Purchase #3 $116.79   10.807%   $129.4115   $129.41   $129.40   $129.40  
  Purchase #4 $232.35   7.776%   $250.4175   $250.42   $250.40   $250.40  
  Purchase #5 $203.61   11.324%   $226.6668   $226.67   $226.65   $226.70  
  Purchase #6 $143.49   9.833%   $157.5994   $157.60   $157.60   $157.60  
  Purchase #7 $171.44   5.841%   $181.4538   $181.45   $181.45   $181.50  
  7 purchase totals = $1,141.82       $1,249.2778   $1,249.28   $1,249.25   $1,249.30