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 $146.88   13.867%   $167.2478   $167.25   $167.25   $167.20  
  Purchase #2 $50.76   11.470%   $56.5822   $56.58   $56.60   $56.60  
  Purchase #3 $236.56   9.817%   $259.7831   $259.78   $259.80   $259.80  
  Purchase #4 $198.83   9.392%   $217.5041   $217.50   $217.50   $217.50  
  Purchase #5 $116.37   7.209%   $124.7591   $124.76   $124.75   $124.80  
  Purchase #6 $248.76   4.119%   $259.0064   $259.01   $259.00   $259.00  
  Purchase #7 $30.27   6.810%   $32.3314   $32.33   $32.35   $32.30  
  7 purchase totals = $1,028.43       $1,117.2141   $1,117.21   $1,117.25   $1,117.20