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 $43.74   8.531%   $47.4715   $47.47   $47.45   $47.50  
  Purchase #2 $223.54   8.630%   $242.8315   $242.83   $242.85   $242.80  
  Purchase #3 $242.87   12.518%   $273.2725   $273.27   $273.25   $273.30  
  Purchase #4 $157.58   7.655%   $169.6427   $169.64   $169.65   $169.60  
  Purchase #5 $235.81   9.161%   $257.4126   $257.41   $257.40   $257.40  
  Purchase #6 $44.60   8.763%   $48.5083   $48.51   $48.50   $48.50  
  Purchase #7 $87.48   11.626%   $97.6504   $97.65   $97.65   $97.70  
  7 purchase totals = $1,035.62       $1,136.7895   $1,136.78   $1,136.75   $1,136.80