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 $208.72   8.723%   $226.9266   $226.93   $226.95   $226.90  
  Purchase #2 $233.88   7.298%   $250.9486   $250.95   $250.95   $250.90  
  Purchase #3 $241.79   5.604%   $255.3399   $255.34   $255.35   $255.30  
  Purchase #4 $155.28   5.229%   $163.3996   $163.40   $163.40   $163.40  
  Purchase #5 $215.53   3.362%   $222.7761   $222.78   $222.80   $222.80  
  Purchase #6 $183.94   5.363%   $193.8047   $193.80   $193.80   $193.80  
  Purchase #7 $244.66   11.436%   $272.6393   $272.64   $272.65   $272.60  
  7 purchase totals = $1,483.80       $1,585.8348   $1,585.84   $1,585.90   $1,585.70