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 $243.51   6.359%   $258.9948   $258.99   $259.00   $259.00  
  Purchase #2 $71.87   4.437%   $75.0589   $75.06   $75.05   $75.10  
  Purchase #3 $241.80   4.788%   $253.3774   $253.38   $253.40   $253.40  
  Purchase #4 $235.92   7.436%   $253.463   $253.46   $253.45   $253.50  
  Purchase #5 $243.71   4.490%   $254.6526   $254.65   $254.65   $254.70  
  Purchase #6 $240.65   3.268%   $248.5144   $248.51   $248.50   $248.50  
  Purchase #7 $47.93   7.523%   $51.5358   $51.54   $51.55   $51.50  
  7 purchase totals = $1,325.39       $1,395.5969   $1,395.59   $1,395.60   $1,395.70