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 $60.99   4.541%   $63.7596   $63.76   $63.75   $63.80  
  Purchase #2 $115.85   9.318%   $126.6449   $126.64   $126.65   $126.60  
  Purchase #3 $74.97   8.436%   $81.2945   $81.29   $81.30   $81.30  
  Purchase #4 $16.70   6.357%   $17.7616   $17.76   $17.75   $17.80  
  Purchase #5 $85.96   13.721%   $97.7546   $97.75   $97.75   $97.80  
  Purchase #6 $206.64   6.731%   $220.5489   $220.55   $220.55   $220.50  
  Purchase #7 $116.66   7.723%   $125.6697   $125.67   $125.65   $125.70  
  7 purchase totals = $677.77       $733.4338   $733.42   $733.40   $733.50