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 $68.81   11.458%   $76.6942   $76.69   $76.70   $76.70  
  Purchase #2 $73.51   5.129%   $77.2803   $77.28   $77.30   $77.30  
  Purchase #3 $38.72   3.343%   $40.0144   $40.01   $40.00   $40.00  
  Purchase #4 $68.91   5.158%   $72.4644   $72.46   $72.45   $72.50  
  Purchase #5 $186.82   3.499%   $193.3568   $193.36   $193.35   $193.40  
  Purchase #6 $179.51   8.870%   $195.4325   $195.43   $195.45   $195.40  
  Purchase #7 $200.37   7.456%   $215.3096   $215.31   $215.30   $215.30  
  7 purchase totals = $816.65       $870.5522   $870.54   $870.55   $870.60