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 $27.51   6.415%   $29.2748   $29.27   $29.25   $29.30  
  Purchase #2 $10.74   3.123%   $11.0754   $11.08   $11.10   $11.10  
  Purchase #3 $167.61   12.251%   $188.1439   $188.14   $188.15   $188.10  
  Purchase #4 $22.63   3.372%   $23.3931   $23.39   $23.40   $23.40  
  Purchase #5 $130.41   5.169%   $137.1509   $137.15   $137.15   $137.20  
  Purchase #6 $75.54   4.164%   $78.6855   $78.69   $78.70   $78.70  
  Purchase #7 $196.62   4.297%   $205.0688   $205.07   $205.05   $205.10  
  7 purchase totals = $631.06       $672.7924   $672.79   $672.80   $672.90