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 $239.46   11.640%   $267.3331   $267.33   $267.35   $267.30  
  Purchase #2 $196.86   4.757%   $206.2246   $206.22   $206.20   $206.20  
  Purchase #3 $146.81   11.363%   $163.492   $163.49   $163.50   $163.50  
  Purchase #4 $16.58   10.737%   $18.3602   $18.36   $18.35   $18.40  
  Purchase #5 $222.73   8.369%   $241.3703   $241.37   $241.35   $241.40  
  Purchase #6 $22.56   8.569%   $24.4932   $24.49   $24.50   $24.50  
  Purchase #7 $130.55   12.495%   $146.8622   $146.86   $146.85   $146.90  
  7 purchase totals = $975.55       $1,068.1356   $1,068.12   $1,068.10   $1,068.20