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 $25.96   9.501%   $28.4265   $28.43   $28.45   $28.40  
  Purchase #2 $186.88   6.422%   $198.8814   $198.88   $198.90   $198.90  
  Purchase #3 $22.69   13.528%   $25.7595   $25.76   $25.75   $25.80  
  Purchase #4 $134.40   4.792%   $140.8404   $140.84   $140.85   $140.80  
  Purchase #5 $203.49   8.499%   $220.7846   $220.78   $220.80   $220.80  
  Purchase #6 $30.91   7.812%   $33.3247   $33.32   $33.30   $33.30  
  Purchase #7 $47.33   8.602%   $51.4013   $51.40   $51.40   $51.40  
  7 purchase totals = $651.66       $699.4184   $699.41   $699.45   $699.40