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 $189.92   5.690%   $200.7264   $200.73   $200.75   $200.70  
  Purchase #2 $247.75   12.401%   $278.4735   $278.47   $278.45   $278.50  
  Purchase #3 $182.45   10.756%   $202.0743   $202.07   $202.05   $202.10  
  Purchase #4 $222.99   13.493%   $253.078   $253.08   $253.10   $253.10  
  Purchase #5 $111.30   4.771%   $116.6101   $116.61   $116.60   $116.60  
  Purchase #6 $18.36   3.162%   $18.9405   $18.94   $18.95   $18.90  
  Purchase #7 $186.27   6.696%   $198.7426   $198.74   $198.75   $198.70  
  7 purchase totals = $1,159.04       $1,268.6454   $1,268.64   $1,268.65   $1,268.60