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 $244.88   3.423%   $253.2622   $253.26   $253.25   $253.30  
  Purchase #2 $200.65   3.158%   $206.9865   $206.99   $207.00   $207.00  
  Purchase #3 $68.35   13.260%   $77.4132   $77.41   $77.40   $77.40  
  Purchase #4 $211.64   7.751%   $228.0442   $228.04   $228.05   $228.00  
  Purchase #5 $203.54   4.149%   $211.9849   $211.98   $212.00   $212.00  
  Purchase #6 $127.33   6.186%   $135.2066   $135.21   $135.20   $135.20  
  Purchase #7 $230.31   3.551%   $238.4883   $238.49   $238.50   $238.50  
  7 purchase totals = $1,286.70       $1,351.3859   $1,351.38   $1,351.40   $1,351.40