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 $216.72   11.348%   $241.3134   $241.31   $241.30   $241.30  
  Purchase #2 $168.54   5.169%   $177.2518   $177.25   $177.25   $177.30  
  Purchase #3 $218.94   5.394%   $230.7496   $230.75   $230.75   $230.70  
  Purchase #4 $192.86   4.352%   $201.2533   $201.25   $201.25   $201.30  
  Purchase #5 $62.79   7.670%   $67.606   $67.61   $67.60   $67.60  
  Purchase #6 $208.39   6.466%   $221.8645   $221.86   $221.85   $221.90  
  Purchase #7 $248.78   11.807%   $278.1535   $278.15   $278.15   $278.20  
  7 purchase totals = $1,317.02       $1,418.1921   $1,418.18   $1,418.15   $1,418.30