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 $243.69   9.172%   $266.0412   $266.04   $266.05   $266.00  
  Purchase #2 $151.47   7.474%   $162.7909   $162.79   $162.80   $162.80  
  Purchase #3 $233.33   11.639%   $260.4873   $260.49   $260.50   $260.50  
  Purchase #4 $199.75   7.446%   $214.6234   $214.62   $214.60   $214.60  
  Purchase #5 $244.50   9.531%   $267.8033   $267.80   $267.80   $267.80  
  Purchase #6 $155.36   12.440%   $174.6868   $174.69   $174.70   $174.70  
  Purchase #7 $115.60   6.373%   $122.9672   $122.97   $122.95   $123.00  
  7 purchase totals = $1,343.70       $1,469.4001   $1,469.40   $1,469.40   $1,469.40