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 $188.78   10.322%   $208.2659   $208.27   $208.25   $208.30  
  Purchase #2 $116.26   5.674%   $122.8566   $122.86   $122.85   $122.90  
  Purchase #3 $53.62   6.203%   $56.946   $56.95   $56.95   $56.90  
  Purchase #4 $246.42   8.364%   $267.0306   $267.03   $267.05   $267.00  
  Purchase #5 $89.59   7.868%   $96.6389   $96.64   $96.65   $96.60  
  Purchase #6 $152.49   11.582%   $170.1514   $170.15   $170.15   $170.20  
  Purchase #7 $38.87   8.434%   $42.1483   $42.15   $42.15   $42.10  
  7 purchase totals = $886.03       $964.0377   $964.05   $964.05   $964.00