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 $232.63   13.310%   $263.5931   $263.59   $263.60   $263.60  
  Purchase #2 $246.93   13.106%   $279.2926   $279.29   $279.30   $279.30  
  Purchase #3 $35.26   8.701%   $38.328   $38.33   $38.35   $38.30  
  Purchase #4 $247.72   8.662%   $269.1775   $269.18   $269.20   $269.20  
  Purchase #5 $194.26   7.308%   $208.4565   $208.46   $208.45   $208.50  
  Purchase #6 $39.48   3.103%   $40.7051   $40.71   $40.70   $40.70  
  Purchase #7 $240.69   7.641%   $259.0811   $259.08   $259.10   $259.10  
  7 purchase totals = $1,236.97       $1,358.6339   $1,358.64   $1,358.70   $1,358.70