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 $55.66   13.169%   $62.9899   $62.99   $63.00   $63.00  
  Purchase #2 $127.85   4.198%   $133.2171   $133.22   $133.20   $133.20  
  Purchase #3 $212.60   13.406%   $241.1012   $241.10   $241.10   $241.10  
  Purchase #4 $21.58   3.359%   $22.3049   $22.30   $22.30   $22.30  
  Purchase #5 $97.92   3.492%   $101.3394   $101.34   $101.35   $101.30  
  Purchase #6 $61.69   11.461%   $68.7603   $68.76   $68.75   $68.80  
  Purchase #7 $213.91   7.737%   $230.4602   $230.46   $230.45   $230.50  
  7 purchase totals = $791.21       $860.1730   $860.17   $860.15   $860.20