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 $84.58   12.626%   $95.2591   $95.26   $95.25   $95.30  
  Purchase #2 $133.34   3.826%   $138.4416   $138.44   $138.45   $138.40  
  Purchase #3 $71.76   11.705%   $80.1595   $80.16   $80.15   $80.20  
  Purchase #4 $96.29   7.202%   $103.2248   $103.22   $103.20   $103.20  
  Purchase #5 $175.40   8.631%   $190.5388   $190.54   $190.55   $190.50  
  Purchase #6 $37.72   8.535%   $40.9394   $40.94   $40.95   $40.90  
  Purchase #7 $101.25   5.169%   $106.4836   $106.48   $106.50   $106.50  
  7 purchase totals = $700.34       $755.0468   $755.04   $755.05   $755.00