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 $237.48   11.214%   $264.111   $264.11   $264.10   $264.10  
  Purchase #2 $162.29   8.292%   $175.7471   $175.75   $175.75   $175.70  
  Purchase #3 $152.61   6.467%   $162.4793   $162.48   $162.50   $162.50  
  Purchase #4 $227.61   13.173%   $257.5931   $257.59   $257.60   $257.60  
  Purchase #5 $162.86   12.509%   $183.2322   $183.23   $183.25   $183.20  
  Purchase #6 $98.57   13.793%   $112.1658   $112.17   $112.15   $112.20  
  Purchase #7 $198.59   4.163%   $206.8573   $206.86   $206.85   $206.90  
  7 purchase totals = $1,240.01       $1,362.1858   $1,362.19   $1,362.20   $1,362.20