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 $191.65   10.274%   $211.3401   $211.34   $211.35   $211.30  
  Purchase #2 $83.83   13.381%   $95.0473   $95.05   $95.05   $95.00  
  Purchase #3 $103.91   13.719%   $118.1654   $118.17   $118.15   $118.20  
  Purchase #4 $40.36   8.637%   $43.8459   $43.85   $43.85   $43.80  
  Purchase #5 $158.53   7.858%   $170.9873   $170.99   $171.00   $171.00  
  Purchase #6 $118.99   11.279%   $132.4109   $132.41   $132.40   $132.40  
  Purchase #7 $215.90   5.858%   $228.5474   $228.55   $228.55   $228.50  
  7 purchase totals = $913.17       $1,000.3443   $1,000.36   $1,000.35   $1,000.20