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 $223.96   11.643%   $250.0357   $250.04   $250.05   $250.00  
  Purchase #2 $65.31   6.174%   $69.3422   $69.34   $69.35   $69.30  
  Purchase #3 $133.31   6.823%   $142.4057   $142.41   $142.40   $142.40  
  Purchase #4 $190.42   7.691%   $205.0652   $205.07   $205.05   $205.10  
  Purchase #5 $237.78   4.511%   $248.5063   $248.51   $248.50   $248.50  
  Purchase #6 $33.28   13.170%   $37.663   $37.66   $37.65   $37.70  
  Purchase #7 $229.35   6.783%   $244.9068   $244.91   $244.90   $244.90  
  7 purchase totals = $1,113.41       $1,197.9249   $1,197.94   $1,197.90   $1,197.90