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 $39.30   5.794%   $41.577   $41.58   $41.60   $41.60  
  Purchase #2 $98.86   11.540%   $110.2684   $110.27   $110.25   $110.30  
  Purchase #3 $29.83   5.503%   $31.4715   $31.47   $31.45   $31.50  
  Purchase #4 $105.79   8.448%   $114.7271   $114.73   $114.75   $114.70  
  Purchase #5 $35.57   9.342%   $38.8929   $38.89   $38.90   $38.90  
  Purchase #6 $225.97   7.466%   $242.8409   $242.84   $242.85   $242.80  
  Purchase #7 $54.54   6.795%   $58.246   $58.25   $58.25   $58.20  
  7 purchase totals = $589.86       $638.0238   $638.03   $638.05   $638.00