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 $218.47   10.746%   $241.9468   $241.95   $241.95   $241.90  
  Purchase #2 $70.90   9.530%   $77.6568   $77.66   $77.65   $77.70  
  Purchase #3 $31.31   5.440%   $33.0133   $33.01   $33.00   $33.00  
  Purchase #4 $114.63   4.373%   $119.6428   $119.64   $119.65   $119.60  
  Purchase #5 $163.28   8.819%   $177.6797   $177.68   $177.70   $177.70  
  Purchase #6 $55.84   3.230%   $57.6436   $57.64   $57.65   $57.60  
  Purchase #7 $114.48   10.589%   $126.6023   $126.60   $126.60   $126.60  
  7 purchase totals = $768.91       $834.1853   $834.18   $834.20   $834.10