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 $49.92   11.626%   $55.7237   $55.72   $55.70   $55.70  
  Purchase #2 $105.70   3.411%   $109.3054   $109.31   $109.30   $109.30  
  Purchase #3 $20.25   6.328%   $21.5314   $21.53   $21.55   $21.50  
  Purchase #4 $197.59   8.595%   $214.5729   $214.57   $214.55   $214.60  
  Purchase #5 $205.32   6.566%   $218.8013   $218.80   $218.80   $218.80  
  Purchase #6 $244.93   7.459%   $263.1993   $263.20   $263.20   $263.20  
  Purchase #7 $202.38   8.168%   $218.9104   $218.91   $218.90   $218.90  
  7 purchase totals = $1,026.09       $1,102.0444   $1,102.04   $1,102.00   $1,102.00