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 $54.46   10.479%   $60.1669   $60.17   $60.15   $60.20  
  Purchase #2 $227.92   6.473%   $242.6733   $242.67   $242.65   $242.70  
  Purchase #3 $110.26   3.448%   $114.0618   $114.06   $114.05   $114.10  
  Purchase #4 $198.35   6.804%   $211.8457   $211.85   $211.85   $211.80  
  Purchase #5 $212.80   5.784%   $225.1084   $225.11   $225.10   $225.10  
  Purchase #6 $50.27   11.348%   $55.9746   $55.97   $55.95   $56.00  
  Purchase #7 $231.68   7.134%   $248.2081   $248.21   $248.20   $248.20  
  7 purchase totals = $1,085.74       $1,158.0388   $1,158.04   $1,157.95   $1,158.10