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 $219.68   11.597%   $245.1563   $245.16   $245.15   $245.20  
  Purchase #2 $77.37   6.822%   $82.6482   $82.65   $82.65   $82.60  
  Purchase #3 $54.92   4.349%   $57.3085   $57.31   $57.30   $57.30  
  Purchase #4 $182.44   12.287%   $204.8564   $204.86   $204.85   $204.90  
  Purchase #5 $61.52   9.261%   $67.2174   $67.22   $67.20   $67.20  
  Purchase #6 $143.69   12.675%   $161.9027   $161.90   $161.90   $161.90  
  Purchase #7 $164.65   7.794%   $177.4828   $177.48   $177.50   $177.50  
  7 purchase totals = $904.27       $996.5723   $996.58   $996.55   $996.60