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 $89.81   7.562%   $96.6014   $96.60   $96.60   $96.60  
  Purchase #2 $33.93   3.412%   $35.0877   $35.09   $35.10   $35.10  
  Purchase #3 $23.74   12.331%   $26.6674   $26.67   $26.65   $26.70  
  Purchase #4 $66.98   4.688%   $70.12   $70.12   $70.10   $70.10  
  Purchase #5 $120.37   6.708%   $128.4444   $128.44   $128.45   $128.40  
  Purchase #6 $164.50   11.494%   $183.4076   $183.41   $183.40   $183.40  
  Purchase #7 $192.34   8.807%   $209.2794   $209.28   $209.30   $209.30  
  7 purchase totals = $691.67       $749.6079   $749.61   $749.60   $749.60