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 $151.75   9.815%   $166.6443   $166.64   $166.65   $166.60  
  Purchase #2 $24.49   12.509%   $27.5535   $27.55   $27.55   $27.60  
  Purchase #3 $208.80   3.617%   $216.3523   $216.35   $216.35   $216.40  
  Purchase #4 $124.61   7.118%   $133.4797   $133.48   $133.50   $133.50  
  Purchase #5 $10.34   4.557%   $10.8112   $10.81   $10.80   $10.80  
  Purchase #6 $75.54   13.463%   $85.71   $85.71   $85.70   $85.70  
  Purchase #7 $187.33   4.757%   $196.2413   $196.24   $196.25   $196.20  
  7 purchase totals = $782.86       $836.7923   $836.78   $836.80   $836.80