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 $162.70   10.384%   $179.5948   $179.59   $179.60   $179.60  
  Purchase #2 $170.95   4.449%   $178.5556   $178.56   $178.55   $178.60  
  Purchase #3 $31.59   10.326%   $34.852   $34.85   $34.85   $34.90  
  Purchase #4 $207.61   5.236%   $218.4805   $218.48   $218.50   $218.50  
  Purchase #5 $128.68   3.728%   $133.4772   $133.48   $133.50   $133.50  
  Purchase #6 $220.93   9.587%   $242.1106   $242.11   $242.10   $242.10  
  Purchase #7 $217.95   13.202%   $246.7238   $246.72   $246.70   $246.70  
  7 purchase totals = $1,140.41       $1,233.7945   $1,233.79   $1,233.80   $1,233.90