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 $52.26   12.113%   $58.5903   $58.59   $58.60   $58.60  
  Purchase #2 $205.48   4.860%   $215.4663   $215.47   $215.45   $215.50  
  Purchase #3 $69.85   8.771%   $75.9765   $75.98   $76.00   $76.00  
  Purchase #4 $142.79   8.475%   $154.8915   $154.89   $154.90   $154.90  
  Purchase #5 $26.62   13.455%   $30.2017   $30.20   $30.20   $30.20  
  Purchase #6 $5.61   12.832%   $6.3299   $6.33   $6.35   $6.30  
  Purchase #7 $75.68   9.169%   $82.6191   $82.62   $82.60   $82.60  
  7 purchase totals = $578.29       $624.0753   $624.08   $624.10   $624.10