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 $61.97   7.393%   $66.5514   $66.55   $66.55   $66.60  
  Purchase #2 $9.67   7.126%   $10.3591   $10.36   $10.35   $10.40  
  Purchase #3 $59.37   3.555%   $61.4806   $61.48   $61.50   $61.50  
  Purchase #4 $123.75   3.865%   $128.5329   $128.53   $128.55   $128.50  
  Purchase #5 $59.82   9.164%   $65.3019   $65.30   $65.30   $65.30  
  Purchase #6 $28.65   3.423%   $29.6307   $29.63   $29.65   $29.60  
  Purchase #7 $240.39   8.582%   $261.0203   $261.02   $261.00   $261.00  
  7 purchase totals = $583.62       $622.8769   $622.87   $622.90   $622.90