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 $112.49   6.310%   $119.5881   $119.59   $119.60   $119.60  
  Purchase #2 $243.64   4.124%   $253.6877   $253.69   $253.70   $253.70  
  Purchase #3 $64.25   11.774%   $71.8148   $71.81   $71.80   $71.80  
  Purchase #4 $242.49   8.823%   $263.8849   $263.88   $263.90   $263.90  
  Purchase #5 $26.71   11.501%   $29.7819   $29.78   $29.80   $29.80  
  Purchase #6 $192.68   7.508%   $207.1464   $207.15   $207.15   $207.10  
  Purchase #7 $97.91   7.345%   $105.1015   $105.10   $105.10   $105.10  
  7 purchase totals = $980.17       $1,051.0053   $1,051.00   $1,051.05   $1,051.00