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 $22.94   8.232%   $24.8284   $24.83   $24.85   $24.80  
  Purchase #2 $135.25   6.516%   $144.0629   $144.06   $144.05   $144.10  
  Purchase #3 $163.99   6.428%   $174.5313   $174.53   $174.55   $174.50  
  Purchase #4 $225.80   6.858%   $241.2854   $241.29   $241.30   $241.30  
  Purchase #5 $115.52   12.631%   $130.1113   $130.11   $130.10   $130.10  
  Purchase #6 $174.75   6.198%   $185.581   $185.58   $185.60   $185.60  
  Purchase #7 $27.58   5.806%   $29.1813   $29.18   $29.20   $29.20  
  7 purchase totals = $865.83       $929.5816   $929.58   $929.65   $929.60