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 $168.70   12.677%   $190.0861   $190.09   $190.10   $190.10  
  Purchase #2 $204.76   9.718%   $224.6586   $224.66   $224.65   $224.70  
  Purchase #3 $240.54   10.539%   $265.8905   $265.89   $265.90   $265.90  
  Purchase #4 $192.41   11.335%   $214.2197   $214.22   $214.20   $214.20  
  Purchase #5 $60.34   12.861%   $68.1003   $68.10   $68.10   $68.10  
  Purchase #6 $184.97   7.581%   $198.9926   $198.99   $199.00   $199.00  
  Purchase #7 $79.60   4.760%   $83.389   $83.39   $83.40   $83.40  
  7 purchase totals = $1,131.32       $1,245.3368   $1,245.34   $1,245.35   $1,245.40