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 $235.36   11.462%   $262.337   $262.34   $262.35   $262.30  
  Purchase #2 $176.36   8.763%   $191.8144   $191.81   $191.80   $191.80  
  Purchase #3 $143.68   10.307%   $158.4891   $158.49   $158.50   $158.50  
  Purchase #4 $42.35   5.381%   $44.6289   $44.63   $44.65   $44.60  
  Purchase #5 $5.27   11.235%   $5.8621   $5.86   $5.85   $5.90  
  Purchase #6 $124.54   5.654%   $131.5815   $131.58   $131.60   $131.60  
  Purchase #7 $165.55   5.830%   $175.2016   $175.20   $175.20   $175.20  
  7 purchase totals = $893.11       $969.9146   $969.91   $969.95   $969.90