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 $237.61   7.147%   $254.592   $254.59   $254.60   $254.60  
  Purchase #2 $55.25   8.212%   $59.7871   $59.79   $59.80   $59.80  
  Purchase #3 $142.43   12.518%   $160.2594   $160.26   $160.25   $160.30  
  Purchase #4 $150.65   13.601%   $171.1399   $171.14   $171.15   $171.10  
  Purchase #5 $236.68   9.861%   $260.019   $260.02   $260.00   $260.00  
  Purchase #6 $229.58   13.702%   $261.0371   $261.04   $261.05   $261.00  
  Purchase #7 $176.91   11.514%   $197.2794   $197.28   $197.30   $197.30  
  7 purchase totals = $1,229.11       $1,364.1139   $1,364.12   $1,364.15   $1,364.10