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 $208.83   8.576%   $226.7393   $226.74   $226.75   $226.70  
  Purchase #2 $127.73   9.128%   $139.3892   $139.39   $139.40   $139.40  
  Purchase #3 $37.55   5.469%   $39.6036   $39.60   $39.60   $39.60  
  Purchase #4 $238.39   11.254%   $265.2184   $265.22   $265.20   $265.20  
  Purchase #5 $84.69   10.126%   $93.2657   $93.27   $93.25   $93.30  
  Purchase #6 $76.36   11.332%   $85.0131   $85.01   $85.00   $85.00  
  Purchase #7 $78.37   3.129%   $80.8222   $80.82   $80.80   $80.80  
  7 purchase totals = $851.92       $930.0515   $930.05   $930.00   $930.00