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 $248.97   10.176%   $274.3052   $274.31   $274.30   $274.30  
  Purchase #2 $51.72   6.246%   $54.9504   $54.95   $54.95   $55.00  
  Purchase #3 $16.61   6.224%   $17.6438   $17.64   $17.65   $17.60  
  Purchase #4 $186.51   11.187%   $207.3749   $207.37   $207.35   $207.40  
  Purchase #5 $34.68   11.677%   $38.7296   $38.73   $38.75   $38.70  
  Purchase #6 $115.32   3.700%   $119.5868   $119.59   $119.60   $119.60  
  Purchase #7 $163.72   6.305%   $174.0425   $174.04   $174.05   $174.00  
  7 purchase totals = $817.53       $886.6332   $886.63   $886.65   $886.60