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 $52.41   3.640%   $54.3177   $54.32   $54.30   $54.30  
  Purchase #2 $192.86   8.181%   $208.6379   $208.64   $208.65   $208.60  
  Purchase #3 $163.74   8.553%   $177.7447   $177.74   $177.75   $177.70  
  Purchase #4 $174.35   9.321%   $190.6012   $190.60   $190.60   $190.60  
  Purchase #5 $33.26   9.106%   $36.2887   $36.29   $36.30   $36.30  
  Purchase #6 $156.99   11.735%   $175.4128   $175.41   $175.40   $175.40  
  Purchase #7 $240.96   6.563%   $256.7742   $256.77   $256.75   $256.80  
  7 purchase totals = $1,014.57       $1,099.7772   $1,099.77   $1,099.75   $1,099.70