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 $163.58   12.234%   $183.5924   $183.59   $183.60   $183.60  
  Purchase #2 $248.29   9.425%   $271.6913   $271.69   $271.70   $271.70  
  Purchase #3 $129.34   6.188%   $137.3436   $137.34   $137.35   $137.30  
  Purchase #4 $136.63   8.118%   $147.7216   $147.72   $147.70   $147.70  
  Purchase #5 $48.30   7.697%   $52.0177   $52.02   $52.00   $52.00  
  Purchase #6 $84.57   13.781%   $96.2246   $96.22   $96.20   $96.20  
  Purchase #7 $153.38   11.182%   $170.531   $170.53   $170.55   $170.50  
  7 purchase totals = $964.09       $1,059.1222   $1,059.11   $1,059.10   $1,059.00