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 $25.35   3.370%   $26.2043   $26.20   $26.20   $26.20  
  Purchase #2 $212.98   5.521%   $224.7386   $224.74   $224.75   $224.70  
  Purchase #3 $225.43   4.103%   $234.6794   $234.68   $234.70   $234.70  
  Purchase #4 $91.43   4.181%   $95.2527   $95.25   $95.25   $95.30  
  Purchase #5 $249.39   9.709%   $273.6033   $273.60   $273.60   $273.60  
  Purchase #6 $133.80   12.856%   $151.0013   $151.00   $151.00   $151.00  
  Purchase #7 $164.71   13.583%   $187.0826   $187.08   $187.10   $187.10  
  7 purchase totals = $1,103.09       $1,192.5622   $1,192.55   $1,192.60   $1,192.60