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 $215.45   13.505%   $244.5465   $244.55   $244.55   $244.50  
  Purchase #2 $233.79   6.234%   $248.3645   $248.36   $248.35   $248.40  
  Purchase #3 $162.65   6.617%   $173.4126   $173.41   $173.40   $173.40  
  Purchase #4 $250.91   3.418%   $259.4861   $259.49   $259.50   $259.50  
  Purchase #5 $175.26   12.817%   $197.7231   $197.72   $197.70   $197.70  
  Purchase #6 $36.57   3.776%   $37.9509   $37.95   $37.95   $38.00  
  Purchase #7 $195.53   11.397%   $217.8146   $217.81   $217.80   $217.80  
  7 purchase totals = $1,270.16       $1,379.2983   $1,379.29   $1,379.25   $1,379.30