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 $204.26   13.141%   $231.1018   $231.10   $231.10   $231.10  
  Purchase #2 $174.68   8.102%   $188.8326   $188.83   $188.85   $188.80  
  Purchase #3 $152.43   10.433%   $168.333   $168.33   $168.35   $168.30  
  Purchase #4 $116.42   7.862%   $125.5729   $125.57   $125.55   $125.60  
  Purchase #5 $193.32   7.841%   $208.4782   $208.48   $208.50   $208.50  
  Purchase #6 $61.38   13.732%   $69.8087   $69.81   $69.80   $69.80  
  Purchase #7 $59.99   8.126%   $64.8648   $64.86   $64.85   $64.90  
  7 purchase totals = $962.48       $1,056.9920   $1,056.98   $1,057.00   $1,057.00