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 $43.92   10.683%   $48.612   $48.61   $48.60   $48.60  
  Purchase #2 $52.65   12.335%   $59.1444   $59.14   $59.15   $59.10  
  Purchase #3 $230.94   4.237%   $240.7249   $240.72   $240.70   $240.70  
  Purchase #4 $161.70   10.799%   $179.162   $179.16   $179.15   $179.20  
  Purchase #5 $160.27   8.120%   $173.2839   $173.28   $173.30   $173.30  
  Purchase #6 $239.88   8.321%   $259.8404   $259.84   $259.85   $259.80  
  Purchase #7 $24.76   5.174%   $26.0411   $26.04   $26.05   $26.00  
  7 purchase totals = $914.12       $986.8087   $986.79   $986.80   $986.70