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 $61.84   12.694%   $69.69   $69.69   $69.70   $69.70  
  Purchase #2 $68.30   12.776%   $77.026   $77.03   $77.05   $77.00  
  Purchase #3 $240.68   6.344%   $255.9487   $255.95   $255.95   $255.90  
  Purchase #4 $100.97   5.248%   $106.2689   $106.27   $106.25   $106.30  
  Purchase #5 $144.90   11.604%   $161.7142   $161.71   $161.70   $161.70  
  Purchase #6 $194.45   12.387%   $218.5365   $218.54   $218.55   $218.50  
  Purchase #7 $171.80   9.868%   $188.7532   $188.75   $188.75   $188.80  
  7 purchase totals = $982.94       $1,077.9375   $1,077.94   $1,077.95   $1,077.90