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 $204.79   9.410%   $224.0607   $224.06   $224.05   $224.10  
  Purchase #2 $10.63   8.813%   $11.5668   $11.57   $11.55   $11.60  
  Purchase #3 $169.56   7.355%   $182.0311   $182.03   $182.05   $182.00  
  Purchase #4 $180.38   5.670%   $190.6075   $190.61   $190.60   $190.60  
  Purchase #5 $183.82   11.538%   $205.0292   $205.03   $205.05   $205.00  
  Purchase #6 $18.90   3.120%   $19.4897   $19.49   $19.50   $19.50  
  Purchase #7 $248.54   12.817%   $280.3954   $280.40   $280.40   $280.40  
  7 purchase totals = $1,016.62       $1,113.1804   $1,113.19   $1,113.20   $1,113.20