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 $61.62   11.440%   $68.6693   $68.67   $68.65   $68.70  
  Purchase #2 $158.87   3.564%   $164.5321   $164.53   $164.55   $164.50  
  Purchase #3 $113.44   11.654%   $126.6603   $126.66   $126.65   $126.70  
  Purchase #4 $90.26   8.293%   $97.7453   $97.75   $97.75   $97.70  
  Purchase #5 $45.72   13.378%   $51.8364   $51.84   $51.85   $51.80  
  Purchase #6 $66.70   12.212%   $74.8454   $74.85   $74.85   $74.80  
  Purchase #7 $151.46   10.149%   $166.8317   $166.83   $166.85   $166.80  
  7 purchase totals = $688.07       $751.1205   $751.13   $751.15   $751.00