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 $60.49   3.801%   $62.7892   $62.79   $62.80   $62.80  
  Purchase #2 $145.94   10.869%   $161.8022   $161.80   $161.80   $161.80  
  Purchase #3 $233.65   6.401%   $248.6059   $248.61   $248.60   $248.60  
  Purchase #4 $228.40   13.674%   $259.6314   $259.63   $259.65   $259.60  
  Purchase #5 $250.97   9.323%   $274.3679   $274.37   $274.35   $274.40  
  Purchase #6 $105.50   8.410%   $114.3726   $114.37   $114.35   $114.40  
  Purchase #7 $60.32   4.472%   $63.0175   $63.02   $63.00   $63.00  
  7 purchase totals = $1,085.27       $1,184.5867   $1,184.59   $1,184.55   $1,184.60