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 $57.96   7.288%   $62.1841   $62.18   $62.20   $62.20  
  Purchase #2 $168.66   8.172%   $182.4429   $182.44   $182.45   $182.40  
  Purchase #3 $87.32   11.720%   $97.5539   $97.55   $97.55   $97.60  
  Purchase #4 $241.35   7.632%   $259.7698   $259.77   $259.75   $259.80  
  Purchase #5 $85.81   7.329%   $92.099   $92.10   $92.10   $92.10  
  Purchase #6 $153.64   4.289%   $160.2296   $160.23   $160.25   $160.20  
  Purchase #7 $202.33   11.116%   $224.821   $224.82   $224.80   $224.80  
  7 purchase totals = $997.07       $1,079.1003   $1,079.09   $1,079.10   $1,079.10