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 $178.41   8.153%   $192.9558   $192.96   $192.95   $193.00  
  Purchase #2 $149.25   9.647%   $163.6481   $163.65   $163.65   $163.60  
  Purchase #3 $246.76   7.388%   $264.9906   $264.99   $265.00   $265.00  
  Purchase #4 $250.90   5.121%   $263.7486   $263.75   $263.75   $263.70  
  Purchase #5 $154.78   13.211%   $175.228   $175.23   $175.25   $175.20  
  Purchase #6 $195.80   9.606%   $214.6085   $214.61   $214.60   $214.60  
  Purchase #7 $194.33   6.257%   $206.4892   $206.49   $206.50   $206.50  
  7 purchase totals = $1,370.23       $1,481.6688   $1,481.68   $1,481.70   $1,481.60