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 $171.95   11.686%   $192.0441   $192.04   $192.05   $192.00  
  Purchase #2 $217.85   11.854%   $243.6739   $243.67   $243.65   $243.70  
  Purchase #3 $198.51   4.784%   $208.0067   $208.01   $208.00   $208.00  
  Purchase #4 $227.63   11.535%   $253.8871   $253.89   $253.90   $253.90  
  Purchase #5 $31.92   7.145%   $34.2007   $34.20   $34.20   $34.20  
  Purchase #6 $51.41   13.177%   $58.1843   $58.18   $58.20   $58.20  
  Purchase #7 $126.66   13.812%   $144.1543   $144.15   $144.15   $144.20  
  7 purchase totals = $1,025.93       $1,134.1511   $1,134.14   $1,134.15   $1,134.20