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 $239.90   5.858%   $253.9533   $253.95   $253.95   $254.00  
  Purchase #2 $117.36   11.772%   $131.1756   $131.18   $131.20   $131.20  
  Purchase #3 $148.85   5.522%   $157.0695   $157.07   $157.05   $157.10  
  Purchase #4 $250.70   7.284%   $268.961   $268.96   $268.95   $269.00  
  Purchase #5 $92.88   3.379%   $96.0184   $96.02   $96.00   $96.00  
  Purchase #6 $84.73   10.479%   $93.6089   $93.61   $93.60   $93.60  
  Purchase #7 $234.64   13.413%   $266.1123   $266.11   $266.10   $266.10  
  7 purchase totals = $1,169.06       $1,266.8990   $1,266.90   $1,266.85   $1,267.00