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 $208.90   13.783%   $237.6927   $237.69   $237.70   $237.70  
  Purchase #2 $23.90   5.286%   $25.1634   $25.16   $25.15   $25.20  
  Purchase #3 $25.49   10.442%   $28.1517   $28.15   $28.15   $28.20  
  Purchase #4 $145.66   6.267%   $154.7885   $154.79   $154.80   $154.80  
  Purchase #5 $171.71   3.357%   $177.4743   $177.47   $177.45   $177.50  
  Purchase #6 $150.97   7.671%   $162.5509   $162.55   $162.55   $162.60  
  Purchase #7 $245.36   4.284%   $255.8712   $255.87   $255.85   $255.90  
  7 purchase totals = $971.99       $1,041.6927   $1,041.68   $1,041.65   $1,041.90