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 $61.90   3.567%   $64.108   $64.11   $64.10   $64.10  
  Purchase #2 $166.81   11.721%   $186.3618   $186.36   $186.35   $186.40  
  Purchase #3 $48.58   13.130%   $54.9586   $54.96   $54.95   $55.00  
  Purchase #4 $229.54   8.590%   $249.2575   $249.26   $249.25   $249.30  
  Purchase #5 $185.99   11.837%   $208.0056   $208.01   $208.00   $208.00  
  Purchase #6 $240.95   13.241%   $272.8542   $272.85   $272.85   $272.90  
  Purchase #7 $156.54   11.793%   $175.0008   $175.00   $175.00   $175.00  
  7 purchase totals = $1,090.31       $1,210.5465   $1,210.55   $1,210.50   $1,210.70