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 $85.57   9.546%   $93.7385   $93.74   $93.75   $93.70  
  Purchase #2 $247.52   5.845%   $261.9875   $261.99   $262.00   $262.00  
  Purchase #3 $77.40   4.845%   $81.15   $81.15   $81.15   $81.20  
  Purchase #4 $65.58   7.403%   $70.4349   $70.43   $70.45   $70.40  
  Purchase #5 $32.98   6.479%   $35.1168   $35.12   $35.10   $35.10  
  Purchase #6 $89.38   8.251%   $96.7547   $96.75   $96.75   $96.80  
  Purchase #7 $71.49   8.841%   $77.8104   $77.81   $77.80   $77.80  
  7 purchase totals = $669.92       $716.9928   $716.99   $717.00   $717.00