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 $49.81   13.111%   $56.3406   $56.34   $56.35   $56.30  
  Purchase #2 $87.44   6.694%   $93.2932   $93.29   $93.30   $93.30  
  Purchase #3 $77.80   10.509%   $85.976   $85.98   $86.00   $86.00  
  Purchase #4 $130.70   8.424%   $141.7102   $141.71   $141.70   $141.70  
  Purchase #5 $15.56   5.353%   $16.3929   $16.39   $16.40   $16.40  
  Purchase #6 $133.37   12.524%   $150.0733   $150.07   $150.05   $150.10  
  Purchase #7 $182.90   13.183%   $207.0117   $207.01   $207.00   $207.00  
  7 purchase totals = $677.58       $750.7979   $750.79   $750.80   $750.80