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 $146.27   12.554%   $164.6327   $164.63   $164.65   $164.60  
  Purchase #2 $50.94   12.297%   $57.2041   $57.20   $57.20   $57.20  
  Purchase #3 $124.63   7.647%   $134.1605   $134.16   $134.15   $134.20  
  Purchase #4 $62.85   10.229%   $69.2789   $69.28   $69.30   $69.30  
  Purchase #5 $243.61   8.355%   $263.9636   $263.96   $263.95   $264.00  
  Purchase #6 $121.79   9.202%   $132.9971   $133.00   $133.00   $133.00  
  Purchase #7 $185.88   3.339%   $192.0865   $192.09   $192.10   $192.10  
  7 purchase totals = $935.97       $1,014.3234   $1,014.32   $1,014.35   $1,014.40