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 $88.43   5.799%   $93.5581   $93.56   $93.55   $93.60  
  Purchase #2 $250.81   10.436%   $276.9845   $276.98   $277.00   $277.00  
  Purchase #3 $93.68   4.766%   $98.1448   $98.14   $98.15   $98.10  
  Purchase #4 $214.95   8.463%   $233.1412   $233.14   $233.15   $233.10  
  Purchase #5 $233.34   6.603%   $248.7474   $248.75   $248.75   $248.70  
  Purchase #6 $210.91   5.845%   $223.2377   $223.24   $223.25   $223.20  
  Purchase #7 $7.85   6.186%   $8.3356   $8.34   $8.35   $8.30  
  7 purchase totals = $1,099.97       $1,182.1493   $1,182.15   $1,182.20   $1,182.00