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 $182.83   12.594%   $205.8556   $205.86   $205.85   $205.90  
  Purchase #2 $218.56   9.337%   $238.9669   $238.97   $238.95   $239.00  
  Purchase #3 $237.68   8.151%   $257.0533   $257.05   $257.05   $257.10  
  Purchase #4 $242.45   5.852%   $256.6382   $256.64   $256.65   $256.60  
  Purchase #5 $249.41   13.465%   $282.9931   $282.99   $283.00   $283.00  
  Purchase #6 $92.80   3.393%   $95.9487   $95.95   $95.95   $95.90  
  Purchase #7 $60.85   8.291%   $65.8951   $65.90   $65.90   $65.90  
  7 purchase totals = $1,284.58       $1,403.3509   $1,403.36   $1,403.35   $1,403.40