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 $145.46   8.352%   $157.6088   $157.61   $157.60   $157.60  
  Purchase #2 $239.43   12.116%   $268.4393   $268.44   $268.45   $268.40  
  Purchase #3 $56.79   13.644%   $64.5384   $64.54   $64.55   $64.50  
  Purchase #4 $177.32   12.312%   $199.1516   $199.15   $199.15   $199.20  
  Purchase #5 $51.81   8.222%   $56.0698   $56.07   $56.05   $56.10  
  Purchase #6 $68.44   9.460%   $74.9144   $74.91   $74.90   $74.90  
  Purchase #7 $237.34   6.133%   $251.8961   $251.90   $251.90   $251.90  
  7 purchase totals = $976.59       $1,072.6184   $1,072.62   $1,072.60   $1,072.60