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 $68.87   11.493%   $76.7852   $76.79   $76.80   $76.80  
  Purchase #2 $133.63   8.346%   $144.7828   $144.78   $144.80   $144.80  
  Purchase #3 $74.50   7.527%   $80.1076   $80.11   $80.10   $80.10  
  Purchase #4 $136.83   8.661%   $148.6808   $148.68   $148.70   $148.70  
  Purchase #5 $174.54   4.277%   $182.0051   $182.01   $182.00   $182.00  
  Purchase #6 $147.52   6.298%   $156.8108   $156.81   $156.80   $156.80  
  Purchase #7 $158.54   12.724%   $178.7126   $178.71   $178.70   $178.70  
  7 purchase totals = $894.43       $967.8849   $967.89   $967.90   $967.90