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 $23.37   13.540%   $26.5343   $26.53   $26.55   $26.50  
  Purchase #2 $90.29   4.609%   $94.4515   $94.45   $94.45   $94.50  
  Purchase #3 $197.30   12.688%   $222.3334   $222.33   $222.35   $222.30  
  Purchase #4 $165.43   12.652%   $186.3602   $186.36   $186.35   $186.40  
  Purchase #5 $124.66   11.180%   $138.597   $138.60   $138.60   $138.60  
  Purchase #6 $206.30   4.307%   $215.1853   $215.19   $215.20   $215.20  
  Purchase #7 $100.27   6.113%   $106.3995   $106.40   $106.40   $106.40  
  7 purchase totals = $907.62       $989.8612   $989.86   $989.90   $989.90