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 $85.88   13.206%   $97.2213   $97.22   $97.20   $97.20  
  Purchase #2 $230.40   10.344%   $254.2326   $254.23   $254.25   $254.20  
  Purchase #3 $87.38   10.722%   $96.7489   $96.75   $96.75   $96.70  
  Purchase #4 $188.96   5.570%   $199.4851   $199.49   $199.50   $199.50  
  Purchase #5 $57.81   10.321%   $63.7766   $63.78   $63.80   $63.80  
  Purchase #6 $165.43   6.687%   $176.4923   $176.49   $176.50   $176.50  
  Purchase #7 $85.30   13.298%   $96.6432   $96.64   $96.65   $96.60  
  7 purchase totals = $901.16       $984.6000   $984.60   $984.65   $984.50