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 $218.27   13.790%   $248.3694   $248.37   $248.35   $248.40  
  Purchase #2 $153.38   6.336%   $163.0982   $163.10   $163.10   $163.10  
  Purchase #3 $230.64   7.271%   $247.4098   $247.41   $247.40   $247.40  
  Purchase #4 $247.64   5.814%   $262.0378   $262.04   $262.05   $262.00  
  Purchase #5 $107.94   9.815%   $118.5343   $118.53   $118.55   $118.50  
  Purchase #6 $150.58   4.218%   $156.9315   $156.93   $156.95   $156.90  
  Purchase #7 $43.47   10.322%   $47.957   $47.96   $47.95   $48.00  
  7 purchase totals = $1,151.92       $1,244.3380   $1,244.34   $1,244.35   $1,244.30