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 $53.39   6.156%   $56.6767   $56.68   $56.70   $56.70  
  Purchase #2 $9.33   6.860%   $9.97   $9.97   $9.95   $10.00  
  Purchase #3 $94.32   7.677%   $101.5609   $101.56   $101.55   $101.60  
  Purchase #4 $174.42   10.225%   $192.2544   $192.25   $192.25   $192.30  
  Purchase #5 $176.29   7.495%   $189.5029   $189.50   $189.50   $189.50  
  Purchase #6 $144.50   11.681%   $161.379   $161.38   $161.40   $161.40  
  Purchase #7 $56.95   8.297%   $61.6751   $61.68   $61.70   $61.70  
  7 purchase totals = $709.20       $773.0190   $773.02   $773.05   $773.20