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 $67.35   5.454%   $71.0233   $71.02   $71.00   $71.00  
  Purchase #2 $238.81   13.670%   $271.4553   $271.46   $271.45   $271.50  
  Purchase #3 $182.59   8.732%   $198.5338   $198.53   $198.55   $198.50  
  Purchase #4 $121.42   3.761%   $125.9866   $125.99   $126.00   $126.00  
  Purchase #5 $144.69   13.559%   $164.3085   $164.31   $164.30   $164.30  
  Purchase #6 $222.87   4.704%   $233.3538   $233.35   $233.35   $233.40  
  Purchase #7 $241.56   4.819%   $253.2008   $253.20   $253.20   $253.20  
  7 purchase totals = $1,219.29       $1,317.8621   $1,317.86   $1,317.85   $1,317.90