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 $215.40   7.823%   $232.2507   $232.25   $232.25   $232.30  
  Purchase #2 $186.69   3.239%   $192.7369   $192.74   $192.75   $192.70  
  Purchase #3 $123.55   8.462%   $134.0048   $134.00   $134.00   $134.00  
  Purchase #4 $78.85   13.256%   $89.3024   $89.30   $89.30   $89.30  
  Purchase #5 $236.45   12.678%   $266.4271   $266.43   $266.45   $266.40  
  Purchase #6 $206.44   6.751%   $220.3768   $220.38   $220.40   $220.40  
  Purchase #7 $55.67   7.129%   $59.6387   $59.64   $59.65   $59.60  
  7 purchase totals = $1,103.05       $1,194.7374   $1,194.74   $1,194.80   $1,194.70