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 $87.60   11.523%   $97.6941   $97.69   $97.70   $97.70  
  Purchase #2 $194.32   6.254%   $206.4728   $206.47   $206.45   $206.50  
  Purchase #3 $77.66   4.448%   $81.1143   $81.11   $81.10   $81.10  
  Purchase #4 $120.86   7.354%   $129.748   $129.75   $129.75   $129.70  
  Purchase #5 $73.73   11.737%   $82.3837   $82.38   $82.40   $82.40  
  Purchase #6 $154.89   3.323%   $160.037   $160.04   $160.05   $160.00  
  Purchase #7 $11.60   12.470%   $13.0465   $13.05   $13.05   $13.00  
  7 purchase totals = $720.66       $770.4964   $770.49   $770.50   $770.40