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 $96.86   7.742%   $104.3589   $104.36   $104.35   $104.40  
  Purchase #2 $215.99   4.116%   $224.8801   $224.88   $224.90   $224.90  
  Purchase #3 $179.58   13.124%   $203.1481   $203.15   $203.15   $203.10  
  Purchase #4 $57.80   5.671%   $61.0778   $61.08   $61.10   $61.10  
  Purchase #5 $68.91   11.469%   $76.8133   $76.81   $76.80   $76.80  
  Purchase #6 $235.77   13.313%   $267.1581   $267.16   $267.15   $267.20  
  Purchase #7 $64.60   10.730%   $71.5316   $71.53   $71.55   $71.50  
  7 purchase totals = $919.51       $1,008.9679   $1,008.97   $1,009.00   $1,009.00