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 $250.97   5.296%   $264.2614   $264.26   $264.25   $264.30  
  Purchase #2 $11.34   4.150%   $11.8106   $11.81   $11.80   $11.80  
  Purchase #3 $62.87   3.384%   $64.9975   $65.00   $65.00   $65.00  
  Purchase #4 $42.91   13.640%   $48.7629   $48.76   $48.75   $48.80  
  Purchase #5 $48.51   5.276%   $51.0694   $51.07   $51.05   $51.10  
  Purchase #6 $208.84   4.694%   $218.6429   $218.64   $218.65   $218.60  
  Purchase #7 $33.59   8.108%   $36.3135   $36.31   $36.30   $36.30  
  7 purchase totals = $659.03       $695.8582   $695.85   $695.80   $695.90