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 $30.69   6.252%   $32.6087   $32.61   $32.60   $32.60  
  Purchase #2 $231.28   11.167%   $257.107   $257.11   $257.10   $257.10  
  Purchase #3 $22.80   8.705%   $24.7847   $24.78   $24.80   $24.80  
  Purchase #4 $237.51   9.874%   $260.9617   $260.96   $260.95   $261.00  
  Purchase #5 $248.55   8.534%   $269.7613   $269.76   $269.75   $269.80  
  Purchase #6 $128.38   6.313%   $136.4846   $136.48   $136.50   $136.50  
  Purchase #7 $230.27   5.791%   $243.6049   $243.60   $243.60   $243.60  
  7 purchase totals = $1,129.48       $1,225.3129   $1,225.30   $1,225.30   $1,225.40