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 $232.58   8.351%   $252.0028   $252.00   $252.00   $252.00  
  Purchase #2 $127.91   5.128%   $134.4692   $134.47   $134.45   $134.50  
  Purchase #3 $116.31   10.283%   $128.2702   $128.27   $128.25   $128.30  
  Purchase #4 $213.31   9.338%   $233.2289   $233.23   $233.25   $233.20  
  Purchase #5 $166.83   8.380%   $180.8104   $180.81   $180.80   $180.80  
  Purchase #6 $67.81   8.509%   $73.58   $73.58   $73.60   $73.60  
  Purchase #7 $132.77   12.349%   $149.1658   $149.17   $149.15   $149.20  
  7 purchase totals = $1,057.52       $1,151.5273   $1,151.53   $1,151.50   $1,151.60