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 $240.88   5.285%   $253.6105   $253.61   $253.60   $253.60  
  Purchase #2 $192.56   11.840%   $215.3591   $215.36   $215.35   $215.40  
  Purchase #3 $69.77   11.309%   $77.6603   $77.66   $77.65   $77.70  
  Purchase #4 $186.48   3.790%   $193.5476   $193.55   $193.55   $193.50  
  Purchase #5 $158.61   5.405%   $167.1829   $167.18   $167.20   $167.20  
  Purchase #6 $237.28   8.158%   $256.6373   $256.64   $256.65   $256.60  
  Purchase #7 $93.61   3.440%   $96.8302   $96.83   $96.85   $96.80  
  7 purchase totals = $1,179.19       $1,260.8279   $1,260.83   $1,260.85   $1,260.80