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 $207.38   4.116%   $215.9158   $215.92   $215.90   $215.90  
  Purchase #2 $225.50   8.806%   $245.3575   $245.36   $245.35   $245.40  
  Purchase #3 $51.37   6.293%   $54.6027   $54.60   $54.60   $54.60  
  Purchase #4 $225.41   10.260%   $248.5371   $248.54   $248.55   $248.50  
  Purchase #5 $154.39   8.353%   $167.2862   $167.29   $167.30   $167.30  
  Purchase #6 $51.91   8.282%   $56.2092   $56.21   $56.20   $56.20  
  Purchase #7 $6.75   5.776%   $7.1399   $7.14   $7.15   $7.10  
  7 purchase totals = $922.71       $995.0484   $995.06   $995.05   $995.00