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 $14.68   10.579%   $16.233   $16.23   $16.25   $16.20  
  Purchase #2 $49.47   12.112%   $55.4618   $55.46   $55.45   $55.50  
  Purchase #3 $55.62   4.485%   $58.1146   $58.11   $58.10   $58.10  
  Purchase #4 $23.49   11.750%   $26.2501   $26.25   $26.25   $26.30  
  Purchase #5 $20.63   10.573%   $22.8112   $22.81   $22.80   $22.80  
  Purchase #6 $57.54   11.609%   $64.2198   $64.22   $64.20   $64.20  
  Purchase #7 $25.70   3.541%   $26.61   $26.61   $26.60   $26.60  
  7 purchase totals = $247.13       $269.7005   $269.69   $269.65   $269.70