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 $68.96   3.841%   $71.6088   $71.61   $71.60   $71.60  
  Purchase #2 $114.80   11.102%   $127.5451   $127.55   $127.55   $127.50  
  Purchase #3 $124.77   3.157%   $128.709   $128.71   $128.70   $128.70  
  Purchase #4 $245.94   5.487%   $259.4347   $259.43   $259.45   $259.40  
  Purchase #5 $224.95   12.137%   $252.2522   $252.25   $252.25   $252.30  
  Purchase #6 $107.79   8.506%   $116.9586   $116.96   $116.95   $117.00  
  Purchase #7 $33.57   13.441%   $38.0821   $38.08   $38.10   $38.10  
  7 purchase totals = $920.78       $994.5905   $994.59   $994.60   $994.60