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 $62.90   6.191%   $66.7941   $66.79   $66.80   $66.80  
  Purchase #2 $221.25   11.493%   $246.6783   $246.68   $246.70   $246.70  
  Purchase #3 $98.90   7.296%   $106.1157   $106.12   $106.10   $106.10  
  Purchase #4 $223.84   8.441%   $242.7343   $242.73   $242.75   $242.70  
  Purchase #5 $176.95   6.474%   $188.4057   $188.41   $188.40   $188.40  
  Purchase #6 $73.85   11.227%   $82.1411   $82.14   $82.15   $82.10  
  Purchase #7 $70.68   10.264%   $77.9346   $77.93   $77.95   $77.90  
  7 purchase totals = $928.37       $1,010.8038   $1,010.80   $1,010.85   $1,010.70