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 $164.50   8.521%   $178.517   $178.52   $178.50   $178.50  
  Purchase #2 $26.72   5.523%   $28.1957   $28.20   $28.20   $28.20  
  Purchase #3 $64.59   5.407%   $68.0824   $68.08   $68.10   $68.10  
  Purchase #4 $132.72   7.212%   $142.2918   $142.29   $142.30   $142.30  
  Purchase #5 $27.58   8.528%   $29.932   $29.93   $29.95   $29.90  
  Purchase #6 $14.54   9.725%   $15.954   $15.95   $15.95   $16.00  
  Purchase #7 $123.60   10.424%   $136.4841   $136.48   $136.50   $136.50  
  7 purchase totals = $554.25       $599.4570   $599.45   $599.50   $599.50