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 $151.53   3.212%   $156.3971   $156.40   $156.40   $156.40  
  Purchase #2 $86.80   8.128%   $93.8551   $93.86   $93.85   $93.90  
  Purchase #3 $33.96   3.825%   $35.259   $35.26   $35.25   $35.30  
  Purchase #4 $217.65   7.313%   $233.5667   $233.57   $233.55   $233.60  
  Purchase #5 $241.57   4.761%   $253.0711   $253.07   $253.05   $253.10  
  Purchase #6 $199.96   13.636%   $227.2265   $227.23   $227.25   $227.20  
  Purchase #7 $180.46   6.320%   $191.8651   $191.87   $191.85   $191.90  
  7 purchase totals = $1,111.93       $1,191.2406   $1,191.26   $1,191.20   $1,191.40