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 $54.49   10.573%   $60.2512   $60.25   $60.25   $60.30  
  Purchase #2 $111.43   10.766%   $123.4266   $123.43   $123.45   $123.40  
  Purchase #3 $95.45   10.685%   $105.6488   $105.65   $105.65   $105.60  
  Purchase #4 $171.26   12.262%   $192.2599   $192.26   $192.25   $192.30  
  Purchase #5 $29.47   9.793%   $32.356   $32.36   $32.35   $32.40  
  Purchase #6 $150.67   4.472%   $157.408   $157.41   $157.40   $157.40  
  Purchase #7 $173.39   11.772%   $193.8015   $193.80   $193.80   $193.80  
  7 purchase totals = $786.16       $865.1520   $865.16   $865.15   $865.20