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 $240.44   10.120%   $264.7725   $264.77   $264.75   $264.80  
  Purchase #2 $172.40   6.127%   $182.9629   $182.96   $182.95   $183.00  
  Purchase #3 $86.95   7.566%   $93.5286   $93.53   $93.55   $93.50  
  Purchase #4 $242.39   3.647%   $251.23   $251.23   $251.25   $251.20  
  Purchase #5 $178.53   10.828%   $197.8612   $197.86   $197.85   $197.90  
  Purchase #6 $170.83   9.326%   $186.7616   $186.76   $186.75   $186.80  
  Purchase #7 $153.42   7.712%   $165.2518   $165.25   $165.25   $165.30  
  7 purchase totals = $1,244.96       $1,342.3686   $1,342.36   $1,342.35   $1,342.50