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 $213.61   13.443%   $242.3256   $242.33   $242.35   $242.30  
  Purchase #2 $172.83   5.661%   $182.6139   $182.61   $182.60   $182.60  
  Purchase #3 $112.84   4.217%   $117.5985   $117.60   $117.60   $117.60  
  Purchase #4 $246.62   5.177%   $259.3875   $259.39   $259.40   $259.40  
  Purchase #5 $76.59   13.205%   $86.7037   $86.70   $86.70   $86.70  
  Purchase #6 $130.52   8.249%   $141.2866   $141.29   $141.30   $141.30  
  Purchase #7 $171.25   3.352%   $176.9903   $176.99   $177.00   $177.00  
  7 purchase totals = $1,124.26       $1,206.9061   $1,206.91   $1,206.95   $1,206.90