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 $57.54   8.197%   $62.2566   $62.26   $62.25   $62.30  
  Purchase #2 $221.81   8.855%   $241.4513   $241.45   $241.45   $241.50  
  Purchase #3 $228.77   9.152%   $249.707   $249.71   $249.70   $249.70  
  Purchase #4 $173.47   8.573%   $188.3416   $188.34   $188.35   $188.30  
  Purchase #5 $53.51   13.130%   $60.5359   $60.54   $60.55   $60.50  
  Purchase #6 $160.88   11.225%   $178.9388   $178.94   $178.95   $178.90  
  Purchase #7 $19.61   4.234%   $20.4403   $20.44   $20.45   $20.40  
  7 purchase totals = $915.59       $1,001.6715   $1,001.68   $1,001.70   $1,001.60