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 $61.32   5.301%   $64.5706   $64.57   $64.55   $64.60  
  Purchase #2 $241.74   9.721%   $265.2395   $265.24   $265.25   $265.20  
  Purchase #3 $9.55   5.314%   $10.0575   $10.06   $10.05   $10.10  
  Purchase #4 $196.85   8.430%   $213.4445   $213.44   $213.45   $213.40  
  Purchase #5 $68.69   12.311%   $77.1464   $77.15   $77.15   $77.10  
  Purchase #6 $12.77   6.565%   $13.6084   $13.61   $13.60   $13.60  
  Purchase #7 $121.74   9.410%   $133.1957   $133.20   $133.20   $133.20  
  7 purchase totals = $712.66       $777.2626   $777.27   $777.25   $777.20