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 $14.27   6.839%   $15.2459   $15.25   $15.25   $15.20  
  Purchase #2 $216.51   10.701%   $239.6787   $239.68   $239.70   $239.70  
  Purchase #3 $25.59   13.232%   $28.9761   $28.98   $29.00   $29.00  
  Purchase #4 $76.60   13.359%   $86.833   $86.83   $86.85   $86.80  
  Purchase #5 $234.30   13.283%   $265.4221   $265.42   $265.40   $265.40  
  Purchase #6 $124.73   8.727%   $135.6152   $135.62   $135.60   $135.60  
  Purchase #7 $29.42   7.212%   $31.5418   $31.54   $31.55   $31.50  
  7 purchase totals = $721.42       $803.3128   $803.32   $803.35   $803.20