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 $146.86   10.635%   $162.4786   $162.48   $162.50   $162.50  
  Purchase #2 $211.72   11.269%   $235.5787   $235.58   $235.60   $235.60  
  Purchase #3 $46.47   7.570%   $49.9878   $49.99   $50.00   $50.00  
  Purchase #4 $19.79   8.874%   $21.5462   $21.55   $21.55   $21.50  
  Purchase #5 $241.26   8.828%   $262.5584   $262.56   $262.55   $262.60  
  Purchase #6 $248.33   7.174%   $266.1452   $266.15   $266.15   $266.10  
  Purchase #7 $188.88   12.740%   $212.9433   $212.94   $212.95   $212.90  
  7 purchase totals = $1,103.31       $1,211.2382   $1,211.25   $1,211.30   $1,211.20