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 $216.41   13.704%   $246.0668   $246.07   $246.05   $246.10  
  Purchase #2 $101.69   13.628%   $115.5483   $115.55   $115.55   $115.50  
  Purchase #3 $41.59   10.390%   $45.9112   $45.91   $45.90   $45.90  
  Purchase #4 $239.67   9.472%   $262.3715   $262.37   $262.35   $262.40  
  Purchase #5 $214.41   13.247%   $242.8129   $242.81   $242.80   $242.80  
  Purchase #6 $13.97   8.280%   $15.1267   $15.13   $15.15   $15.10  
  Purchase #7 $197.48   13.156%   $223.4605   $223.46   $223.45   $223.50  
  7 purchase totals = $1,025.22       $1,151.2979   $1,151.30   $1,151.25   $1,151.30