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 $24.58   6.420%   $26.158   $26.16   $26.15   $26.20  
  Purchase #2 $214.67   11.128%   $238.5585   $238.56   $238.55   $238.60  
  Purchase #3 $136.26   12.707%   $153.5746   $153.57   $153.55   $153.60  
  Purchase #4 $82.68   6.711%   $88.2287   $88.23   $88.25   $88.20  
  Purchase #5 $85.44   12.456%   $96.0824   $96.08   $96.10   $96.10  
  Purchase #6 $193.53   6.856%   $206.7984   $206.80   $206.80   $206.80  
  Purchase #7 $164.94   13.542%   $187.2762   $187.28   $187.30   $187.30  
  7 purchase totals = $902.10       $996.6768   $996.68   $996.70   $996.80