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 $62.96   3.236%   $64.9974   $65.00   $65.00   $65.00  
  Purchase #2 $189.30   13.558%   $214.9653   $214.97   $214.95   $215.00  
  Purchase #3 $242.49   4.247%   $252.7886   $252.79   $252.80   $252.80  
  Purchase #4 $191.70   5.154%   $201.5802   $201.58   $201.60   $201.60  
  Purchase #5 $144.61   8.364%   $156.7052   $156.71   $156.70   $156.70  
  Purchase #6 $236.30   5.683%   $249.7289   $249.73   $249.75   $249.70  
  Purchase #7 $101.56   11.283%   $113.019   $113.02   $113.00   $113.00  
  7 purchase totals = $1,168.92       $1,253.7846   $1,253.80   $1,253.80   $1,253.80