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 $54.75   10.298%   $60.3882   $60.39   $60.40   $60.40  
  Purchase #2 $246.85   5.308%   $259.9528   $259.95   $259.95   $260.00  
  Purchase #3 $169.39   9.353%   $185.233   $185.23   $185.25   $185.20  
  Purchase #4 $107.88   5.373%   $113.6764   $113.68   $113.70   $113.70  
  Purchase #5 $168.55   9.160%   $183.9892   $183.99   $184.00   $184.00  
  Purchase #6 $200.28   3.225%   $206.739   $206.74   $206.75   $206.70  
  Purchase #7 $107.50   9.328%   $117.5276   $117.53   $117.55   $117.50  
  7 purchase totals = $1,055.20       $1,127.5062   $1,127.51   $1,127.60   $1,127.50