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 $158.97   4.258%   $165.7389   $165.74   $165.75   $165.70  
  Purchase #2 $85.99   7.451%   $92.3971   $92.40   $92.40   $92.40  
  Purchase #3 $68.74   13.137%   $77.7704   $77.77   $77.75   $77.80  
  Purchase #4 $195.42   6.310%   $207.751   $207.75   $207.75   $207.80  
  Purchase #5 $82.96   8.681%   $90.1618   $90.16   $90.15   $90.20  
  Purchase #6 $119.62   3.623%   $123.9538   $123.95   $123.95   $124.00  
  Purchase #7 $248.33   9.434%   $271.7575   $271.76   $271.75   $271.80  
  7 purchase totals = $960.03       $1,029.5305   $1,029.53   $1,029.50   $1,029.70