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 $202.35   12.128%   $226.891   $226.89   $226.90   $226.90  
  Purchase #2 $89.44   13.849%   $101.8265   $101.83   $101.85   $101.80  
  Purchase #3 $46.67   6.466%   $49.6877   $49.69   $49.70   $49.70  
  Purchase #4 $172.25   10.172%   $189.7713   $189.77   $189.75   $189.80  
  Purchase #5 $175.47   3.112%   $180.9306   $180.93   $180.95   $180.90  
  Purchase #6 $249.89   6.830%   $266.9575   $266.96   $266.95   $267.00  
  Purchase #7 $235.70   3.336%   $243.563   $243.56   $243.55   $243.60  
  7 purchase totals = $1,171.77       $1,259.6276   $1,259.63   $1,259.65   $1,259.70