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 $242.52   10.763%   $268.6224   $268.62   $268.60   $268.60  
  Purchase #2 $107.72   13.488%   $122.2493   $122.25   $122.25   $122.20  
  Purchase #3 $115.40   6.323%   $122.6967   $122.70   $122.70   $122.70  
  Purchase #4 $156.65   7.122%   $167.8066   $167.81   $167.80   $167.80  
  Purchase #5 $122.26   13.557%   $138.8348   $138.83   $138.85   $138.80  
  Purchase #6 $121.69   3.467%   $125.909   $125.91   $125.90   $125.90  
  Purchase #7 $151.77   13.479%   $172.2271   $172.23   $172.25   $172.20  
  7 purchase totals = $1,018.01       $1,118.3459   $1,118.35   $1,118.35   $1,118.20