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 $202.62   10.697%   $224.2943   $224.29   $224.30   $224.30  
  Purchase #2 $214.73   9.284%   $234.6655   $234.67   $234.65   $234.70  
  Purchase #3 $238.87   5.115%   $251.0882   $251.09   $251.10   $251.10  
  Purchase #4 $60.51   4.497%   $63.2311   $63.23   $63.25   $63.20  
  Purchase #5 $174.96   8.627%   $190.0538   $190.05   $190.05   $190.10  
  Purchase #6 $174.93   7.528%   $188.0987   $188.10   $188.10   $188.10  
  Purchase #7 $30.68   4.771%   $32.1437   $32.14   $32.15   $32.10  
  7 purchase totals = $1,097.30       $1,183.5753   $1,183.57   $1,183.60   $1,183.60