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 $226.87   6.503%   $241.6234   $241.62   $241.60   $241.60  
  Purchase #2 $176.51   8.311%   $191.1797   $191.18   $191.20   $191.20  
  Purchase #3 $202.90   11.526%   $226.2863   $226.29   $226.30   $226.30  
  Purchase #4 $241.87   3.529%   $250.4056   $250.41   $250.40   $250.40  
  Purchase #5 $46.42   4.842%   $48.6677   $48.67   $48.65   $48.70  
  Purchase #6 $228.79   11.475%   $255.0437   $255.04   $255.05   $255.00  
  Purchase #7 $232.96   7.390%   $250.1757   $250.18   $250.20   $250.20  
  7 purchase totals = $1,356.32       $1,463.3821   $1,463.39   $1,463.40   $1,463.40