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 $49.87   10.166%   $54.9398   $54.94   $54.95   $54.90  
  Purchase #2 $76.73   3.520%   $79.4309   $79.43   $79.45   $79.40  
  Purchase #3 $50.78   6.831%   $54.2488   $54.25   $54.25   $54.20  
  Purchase #4 $23.25   6.104%   $24.6692   $24.67   $24.65   $24.70  
  Purchase #5 $11.96   7.358%   $12.84   $12.84   $12.85   $12.80  
  Purchase #6 $222.71   8.555%   $241.7628   $241.76   $241.75   $241.80  
  Purchase #7 $234.70   12.433%   $263.8803   $263.88   $263.90   $263.90  
  7 purchase totals = $670.00       $731.7718   $731.77   $731.80   $731.70