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 $222.73   12.711%   $251.0412   $251.04   $251.05   $251.00  
  Purchase #2 $107.75   7.194%   $115.5015   $115.50   $115.50   $115.50  
  Purchase #3 $157.40   12.776%   $177.5094   $177.51   $177.50   $177.50  
  Purchase #4 $66.83   6.578%   $71.2261   $71.23   $71.25   $71.20  
  Purchase #5 $179.86   3.286%   $185.7702   $185.77   $185.75   $185.80  
  Purchase #6 $168.81   12.641%   $190.1493   $190.15   $190.15   $190.10  
  Purchase #7 $61.34   13.651%   $69.7135   $69.71   $69.70   $69.70  
  7 purchase totals = $964.72       $1,060.9112   $1,060.91   $1,060.90   $1,060.80